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AUSTRALIAN
BIRDS
Journal of the
NSW FIELD ORNITHOLOGISTS CLUB Inc.
Volume 28 Supplement October 1994
Large Forest Owls
of
New South Wales
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BIRDS
Volume 28 Supplement October 1994
GENERAL INTRODUCTION
S.J.S. DEBUS
The large Australian forest owls have been little known until the last decade. Fleay (1968)
and Schodde & Mason (1980) first articulated the dependence of the Powerful Owl Ninox strenua
and Sooty Owl Tyto tenebricosa on mature forest, large tree hollows for nesting and roosting, and
hollow -dependent arboreal marsupials as important prey. This was developed further with the
suggestion that these owls may be dependent on old forest, and adversely affected by its conversion
to regrowth during forestry operations (e.g. Blakers et al. 1984; Loyn 1985). In 1988 Davey &
Norton (1990) identified the large forest owls as a group specifically requiring research and
management, in order to assist the development of ecologically sustainable timber -harvesting
strategies and thus conserve the wildlife values of publicly owned wood -production forests. From
there, several owl projects developed concurrently: Sooty Owl in southern Victoria (Milledge et al.
1991); Powerful Owl in inland Victoria (Trail) 1993); all three species (including the Masked Owl
Tyto novaehollandiae) in southern New South Wales (Davey 1993; Kavanagh & Peake 1993).
Also concurrently, an owl project was being developed in northern New South Wales by the
University of New England (UNE); this project was originated by Hugh Ford.
The background and rationale for the UNE project are given in the following Sooty Owl
review. Although the UNE project was conceived specifically as a Sooty Owl survey, the other
two owl species were included as primary target species from the start of field work.
A necessary part of the overall process was a detailed literature and museum review of
knowledge on the three owl species. This process proved to be a collaborative effort, the results of
which appear in the following three species reviews. Tony Rose responded generously with his
unpublished dietary and specimen data and other observations on the Masked Owl, following my
appeal for information in a preliminary note on this species (Debus 1990); the result is the jointly
authored Masked Owl review herein. During the project Chris Chafer submitted a detailed
observational and review paper on the Powerful Owl. His original observations appeared as a
separate paper (Chafer 1992); much of the remainder appears in the jointly authored Powerful Owl
review herein, to which Chris contributed some of the tables and all of the graphs and statistical
analyses. Chris also contributed the graphs and statistical analyses to the following Sooty Owl
review.
Australian Birds Vol. 28 Supplement SiThis series of review papers provides the historical background on the distribution, habitat,
biology and perceived status of the Sooty, Powerful and Masked Owls. It includes field work
conducted by other researchers up to 1989-90 and published over subsequent years, and incidental
(published) records to the end of 1992. This series of reviews was intended to present the state of
knowledge as at the start of the UNE project, but events have overtaken its completion; it is
inappropriate and impossible to ignore other work published in the interim. The literature cited in
these reviews has been combined in a common reference list at the end.
ACKNOWLEDGEMENTS
I thank those who facilitated research on all three owl species. Ian McAllan provided the
blank map ofNSW ten-minute grids, from the NSW Bird Atlas, and assisted with historical research.
Alan Morris provided advance copies of the 1989-91 FOC bird reports. Walter Boles provided
access to specimens and data in The Australian Museum. Owl surveys in northern NSW were
supported by World Wide Fund for Nature Australia (Project 142) and the (then) Australian National
Parks & Wildlife Service (Endangered Species Program, Project 41). Library and museum research
was supported by a Cayley Memorial Scholarship, administered by the Gould League of NSW.
Funding support for this special issue was generously provided by World Wide Fund for Nature
Australia and Australian Nature Conservation Agency. Thanks also to Steve Tredinnick for specially
providing the marvellous sketches for this issue.
S2 October 1994Sooty Owl with Sugar Glider Petaurus breviceps
Sketch: Steve Tredinnick
Australian Birds Vol. 28 Supplement S3THE SOOTY OWL Tyto tenebricosa IN NEW SOUTH WALES
S.J.S. DEBUS
Zoology Department, University of New England, Armidale 2351
SUMMARY
Records of the Sooty Owl Tyto tenebricosa were collated (n=226), and associated literature
reviewed, in order to assess the Owl’s distribution, habitat, biology and perceived status in New
South Wales. This provides the historical context for a field survey of the Owl’s distribution, status
and habitat requirements in north-east NSW 1990-92, in relation to forest management. It is
concluded that: (1) the Owl’s perceived status has been depressed by its cryptic habits, dense and
remote habitat, and low observer effort; (2) that it occurs in three populations in NSW, with a wider
altitudinal tolerance in the north; (3) its major dietary components are Common Ringtail Possum
Pseudocheirus peregrinus, Sugar Glider Petaurus breviceps and rats (prey 75% arboreal mammals
by biomass, none restricted to old -growth forest); (4) its breeding productivity in the wild may be
limited by food supply.
INTRODUCTION
In mid 1988 H.A. Ford, H.F. Recher and I planned a project on the distribution, status and
habitat requirements of the Sooty Owl Tyto tenebricosa in northern New South Wales. The need
for this project was predicated on the assumption that, as top predators, large forest owls occur at
low densities and may be vulnerable to fragmentation of their habitat. We considered that if a top
predator such as the Sooty Owl could be conserved adequately, then many other species sharing its
ecosystem would also be conserved. Furthermore, a good population of Sooty Owls might indicate
a diverse and abundant supply of arboreal mammals, and probably a healthy forest.
We chose the Sooty Owl because it is a specialised inhabitant of closed forest (rainforest)
and tall open forest, which is limited in area in south-eastern Australia, and therefore has a low total
population size. In south-eastern Australia, the Sooty Owl was recorded in only 14 one -degree
squares during the Atlas of Australian Birds project (Blakers et al. 1984). Estimated or inferred
home -ranges of 2-8 km2 per pair (from Schodde & Mason 1980) suggested that, optimistically
assuming 10% of each square holds suitable habitat all of which is occupied (i.e. 14 000 km2), there
might be 2000 to 7000 pairs of Sooty Owls. In NSW there were records from seven atlas squares
and only one breeding record, suggesting a population of 1000 to 3500 pairs in the State. These
figures from our working hypothesis suggested that the Sooty Owl shows many parallels with the
Spotted Owl Strix occidentalis of North America: similar population sizes; home -range sizes;
apparent requirements for “old” forest including large tree holes; presumed susceptibility to habitat
modification; and poor dispersal as evidenced by subspeciation (or speciation in the case of the
Sooty Owl complex: Schodde & Mason 1980). These are features that make a species vulnerable.
Projections have predicted a decline and successive extinction of small, isolated populations of the
Spotted Owl, which is considered endangered; it has therefore generated much research on the
effects of forestry practices (e.g. Dawson et al. 1987; Simberloff 1989; Shields & King 1990;
Lamberson et al. 1992; Carey et al. 1992). The expansion of logging into old -growth forest, and a
possible wood -chip industry in northern NSW, suggested the need for similar research on the
Sooty Owl.
S4 October 1994Field work for the Sooty Owl project was undertaken over three years 1990-92 inclusive.
The survey included the other large forest owls, the Powerful Owl Ninox strenua and Masked Owl
Tyto novaehollandiae, on the grounds that they may also be affected by logging and clearing. The
survey results will be presented elsewhere.
Data on the Sooty Owl’s diet in NSW are limited to contemporary samples or incidental
records from nine locations (Fleay 1968; Hyem 1979; Smith 1984; Hollands 1991; Kavanagh
1992; Lundie-Jenkins 1993; Chafer & Anderson 1994; Holmes 1994). Subfossil samples from two
sites are now presumed referable to the Sooty Owl (Hall 1977; Hollands 1991), but may have been
deposited by more than one owl species and in any case it is the Owl’s present-day diet that is of
most concern. Data on diet may be important for inferring the Owl’s hunting habitat, foraging
zone, and the resource requirements (e.g. den sites) of its prey species (e.g. Kavanagh 1992; Debus
& Rose, this issue); diet and food supply are likely to be the most important factor in the Owl’s
ecology (cf. Carey et al. 1992 on Spotted Owl).
Data on the Sooty Owl’s breeding biology in NSW are also limited, but available information
may be similarly useful for inferring the Owl’s requirements.
METHODS
Data or inferences on the Sooty Owl’s broad distribution, status, habitat and biology were
collated from the literature. Specific records in New South Wales were extracted from published
sightings to 1992, museums (Australian Museum, South Australian Museum), the Royal Australasian
Ornithologists Union Atlas of Australian Birds (unusual record forms), the Australian Bird Banding
Scheme, the Keith Hindwood Bird Recording Service (per E.S. Hoskin), and colleagues’ unpublished
notes. Literature records were obtained from the following sources (details in Appendix 1): Emu;
Corella; Australian Birds; the NSW Field Ornithologists Club annual bird reports 1970-91 inclusive;
NSW FOC Newsletter (“unusual records” series by Morris & Chafer) for 1989-92 inclusive;
Cumberland Bird Obervers Club Newsletter (members’ sightings inserts); books, reports and other
publications (Gould 1848, 1865; Hindwood & McGill 1958; Fleay 1968; Holmes 1987; Gibson
1989; Hollands 1991; Hoskin et al. 1991; Davey 1993; Kavanagh & Peake 1993). Some records
were reported by more than one source, therefore care was taken not to double -count records. One
record was taken as one bird at one locality in one year (i.e. two birds = two records), and nestlings
were not counted. Data were analysed as the number of sites at which the Sooty Owl has been
recorded, a “site” being defined as the area within which clusters of records can be reasonably
assumed to represent a single occupied Owl territory. Published and unpublished records of the
Sooty Owl in NSW are listed in Appendix 1, except for those obtained during the field survey or by
colleagues during concurrent or subsequent (as yet unpublished) work.
Sooty Owl records were sorted into the botanic zones of Anderson (1961), as adopted by
McAl Ian & Bruce (1989), and differences in the frequency of records between zones were tested by
the log -likelihood ratio test (G- test: Zar 1984; tests run by C.J. Chafer). Preliminary statistical
analysis of Sooty Owl sites against altitude and latitude, and within physiographic provinces, was
kindly performed by C.J. Chafer as a basis for further biogeographic analysis (Chafer in prep.).
Physiographic provinces (see Jennings & Mabbutt 1986) are regions of broadly uniform geology,
topography and climate, and hence vegetation. It must be acknowledged that it was Chafer who
suggested using the physiographic provinces to analyse Sooty Owl records, and who performed the
associated tasks listed hereunder. To quote Chafer, physiography determines the ecological
landscape: vegetation structure and floristics, and hence other biota, are an evolutionary function
of the underlying geomorphological matrix and climatic/weathering regimes through time (see
Debus & Chafer, this issue). Altitudes were estimated from topographic maps for 109 sufficiently
precise locations, and plotted against ranked latitudinal position (Spearman’s Rank Correlation
Australian Birds Vol. 28 Supplement S5Coefficient: Zar 1984). Altitudes of sites were also ranked within the three coastal physiographic
provinces of NSW as given by Jennings & Mabbutt (1986), and differences tested by the Kruskal-
Wallis test and Tukey-type multiple comparisons test using Dunn’s equation (Zar 1984). Spearman
and Kruskal-Wallis tests were conducted using Statview 512+ (Feldman et al. 1988), and the multiple
comparisons tests were conducted manually. Sooty Owl sites were also located on geological
maps, to assess whether there was any pattern of Owl occurrence with geological substrate.
HISTORICAL BACKGROUND
The Sooty Owl has traditionally been considered rare (McGill 1960; Fleay 1968; Macdonald
1973) or at least rarely seen (Calaby 1976), restricted in range and elusive (Fleay 1968). This view
of rarity has persisted (Fleay 1981; Slater etal. 1986), although increasing familiarity with the bird
has suggested otherwise. Hyem (1979) found it more numerous than the Powerful or Masked Owl,
with nine Sooty Owl pairs in a quadrant of 10-15 km radius; he described it as widely distributed in
suitable localities (a mosaic of tall open forest and gully rainforest). Pizzey (1980) conceded that it
is perhaps more common than records suggest, but one of the least known Australian raptors.
Beruldsen (1980) noted that it is difficult to locate, can be found by searching, and is probably not
as rare as records indicate. Fleay (1981) noted that it has “avoided attention for a long time”. That
is, its perceived rarity was partly a detection problem (see also Beruldsen 1986).
The traditional view of the Sooty Owl’s range and habitat has been the tall open forest (wet
sclerophyll) and closed forest (rainforest) of the east coast and Great Dividing Range escarpment,
particularly wet gullies (e.g. McGill 1960; Fleay 1968; Slater 1970; Calaby 1976; Pizzey 1980).
However, there is one report from coastal dune scrub (Morris 1975). Fleay (1968) considered that
Sooty Owls roost primarily in “giant” hollow trees, and only exceptionally in dense vegetation
when guarding fledglings. Later authors conceded that the Owls sometimes roost in dense vegetation
(Slater 1970; Calaby 1976; Pizzey 1980), and Hyem (1979) found that in rainforest gullies they
often do so preferentially. There was one anecdotal report that Sooty Owls sometimes roost in
caves (Calaby 1976). Typical Sooty Owl nest sites have been described as vertical hollows in tree
trunks, in gullies of thickly forested hilly or mountainous country (Beruldsen 1980).
The foregoing resulted in a standard reference on Australian owls (Schodde & Mason
1980) characterising the Sooty Owl as: uncommon, rarely seen, and restricted to the coast and
adjacent slopes of the Divide; in gully rainforest with emergent mature eucalypts and a dense
substorey, pairs holding home -ranges of 200-800 ha; and roosting in large tree hollows, the
“chimneys” of figs Ficus sp., or on shaded branches low in dense gully rainforest. Subsequent
work has continued to modify this view. Morris et al. (1981) classified the Sooty Owl as
“uncommon” in NSW, defined as an estimated population of 1000-10 000 birds in the State. Fleay
(1979, 1981) found that the Sooty Owl has a high reproductive potential: captive birds can breed at
any time of the year, and raise two broods per year of up to three young per brood on a plentiful
food supply; they can breed at one year old. Blakers et al. (1984) noted that Sooty Owls can be
seen hunting along roads and grassy areas adjoining forest where the habitat is altered, and that
increased familiarity with their calls has resulted in detection in many places where they were
believed absent. Smith (1984) and Loyn etal. (1986) cited further examples of the Owls regularly
roosting in dense foliage in gully rainforest. Schodde & Tidemann (1986) noted that roost sites
may include crevices under banks or cliffs. McAllan & Bruce (1989) attributed a lack of records
partly to a lack of night observations. O’Brien (1990) found the Sooty Owl “uncommon” but more
numerous than expected, owing to its loud and recognisable call and its ready response to tape
playback. Hollands (1991) found that Sooty Owls sometimes range into drier forest to hunt, and
that they roost and even nest in caves in forest lacking suitable sites. He noted that the difficulty of
locating the birds makes population assessment difficult, and that the species is rarely seen and
seldom heard because there are few people about at night in its habitat. Finally, systematic surveys
S6 Debus : Sooty Owl October 1994using appropriate methods have resulted in many Sooty Owl records, sometimes more than for
Masked or Powerful Owls; Sooty Owls have been found in the more moist spectrum of “dry”
sclerophyll forest, and also roosting frequently in dense rainforest foliage and occasionally in caves
and under rock overhangs in gorges (Milledge et al. 1991, 1993; Kavanagh 1992; Davey 1993;
Kavanagh & Peake 1993; Chafer & Anderson 1994). Lundie-Jenkins (1993) also found roost sites
“in the cliffs” above a creek gully, presumably in shallow sandstone recesses. These records suggest
that cave -roosting is common in this species, and that cave deposits of large Tyto pellets (and
indeed sightings of large, dark Tyto owls in caves) in coastal eastern Australia should not be
automatically ascribed to the Masked Owl.
One survey found the Sooty Owl locally extinct (restricted or of patchy occurrence in
remnants) in an extensively cleared area of former subtropical rainforest (the “Big Scrub”: Holmes
1987). This was the largest patch of such habitat in NSW, and may have supported a large breeding
population of Sooty Owls. Holmes found the Owl at only two sites of 23 and 60 ha of rainforest
enclosed within extensive eucalypt forest of the Nightcap Range of c. 16 000 ha, but not in any
small, isolated remnants <25 ha, 8-33 km from the Nightcap Range, nor in large (60-80 ha) remnants 23-29 km from the Nightcap Range. However, there is one case of a Sooty Owl dispersing 50 km (Anon. 1991), at least partly across cleared (wet, formerly forested) country. The Sooty Owl’s diet has been considered to consist mainly of arboreal marsupials, some of which require tree hollows as den sites (e.g. Schodde & Mason 1980; Smith 1984). However, the Owl can shift from arboreal to terrestrial prey according to availability (Loyn et aL 1986). Recent work has shown a range of terrestrial as well as arboreal prey (Hollands 1991; Kavanagh 1992; Lundie-Jenkins 1993; Chafer & Anderson 1994). In one area the Sooty Owl is a more generalised predator than Masked or Powerful Owl, with half of its prey terrestrial by number and virtually none restricted to old -growth forest (Kavanagh 1992). In another area terrestrial prey is said to predominate (Lundie-Jenkins 1993), although the major prey species at that site (the introduced Black Rat Rattus rattus) is scansorial (Strahan 1983). At other sites this rat has also featured prominently in prey samples (Hyem 1979; Hollands 1991; Chafer & Anderson 1994). Occasional prey records include the introduced Rabbit Oryctolagus cuniculus (Hollands 1991; Kavanagh 1992), which can penetrate deep into forest along logging roads (pers. obs.). By the time field work was underway for the owl project in northern NSW, it was apparent from previous and concurrent work that the Sooty Owl is somewhat more numerous and more flexible in diet and habitat requirements (including roost and nest sites) than previously believed. Furthermore, it has some of the inherent Tyto flexibility in breeding and a potentially high recruitment rate (variable breeding season and clutch size in relation to prey abundance, e.g. Schodde & Mason 1980). The Sooty Owl has been classified nationally as “rare” (Garnett 1992), and in New South Wales as “vulnerable and rare” (Schedule 12, Part 2 of the National Parks & Wildlife Act). DISTRIBUTION IN NEW SOUTH WALES The Sooty Owl occupies a narrow strip on the coast and eastern fall of the tablelands in NSW (Figure 1). An analysis of 226 records (134 sites) adds the Central and Southern Tablelands to the list of NSW regions in which the Sooty Owl has been recorded (cf. Morris etal. 1981). Using the regions of McAllan & Bruce (1989), which are based on botanical provinces, 74% of sites were in coastal regions and 26% on the tablelands (n = 134 sites). This difference is significant for 109 precise locations (G2=7.741, P=0.021). The regional breakdown is as follows: North Coast 41 sites (31%); Central Coast 31 (23%); South Coast 27 (20%); Northern Tablelands 26 (19%); Central Tablelands 5 (4%); Southern Tablelands 4 (3%). Australian Birds Vol. 28 Supplement S7153° 150° 151° 152′ 149* .01 141° 142° 143° 144′ 145′ 146° 147* 148° II WI W 29′ Fiji 30′ 1+1 31′ II 32′ 33′ 34* Jr- 35* p 36′ 37° Figure 1. Map of New South Wales, showing distribution of Sooty Owl in ten-minute grids. Totals for the Northern Tablelands and North Coast largely reflect the survey work of G. Holmes, reported in the NSW FOC annual bird reports, and the work of Goddard (in Fleay 1968) and Hyem (1979). There is a break in distribution at the cleared Hunter Valley (McAllan & Bruce 1989), parts of which may have been too dry and open for the Owl although rainforest formerly extended inland to Maitland and the Barrington Tops (I. McAllan pers. comm.). Most records for the Hunter area come from the Central Coast adjoining the southern side, and reflect the work of O’Brien (1990). There is another apparent break at the Shoalhaven Valley, although this may partly reflect the lack of surveys. Records for the South Coast reflect recent survey work there (Kavanagh 1992; Davey 1993; Kavanagh & Peake 1993). Most records for the Central Coast are from the Illawarra and Gosford districts. The low total for the Sydney district, despite the concentration of observers there, suggests a local break in distribution perhaps caused partly by the suburbs. The Sydney Basin (sandstone and shale dry forests) contained some unsuitable habitat, but most of the northern suburbs were covered in tall Blue Gum Eucalyptus saligna and Blackbutt E. pilularis forest with some rainforest patches (Benson & Howell 1990). Most Sydney records come from the Royal National Park; there was an early specimen from Manly (AM 0.13397, registered 1904) and a sighting in a side gully of the upper Lane Cove Valley in 1960 (Hoskin et al. 1991), but no recent records. The species has become locally extinct in parts of the North Coast: specimens were taken from the Richmond and Clarence Valleys, now cleared (Gould 1865; AM A.1173 and AM 0.18279, registered in 1877 and 1904), and it is now absent from remnants of the formerly extensive Big Scrub (Holmes 1987). S8 Debus : Sooty Owl October 19941600 1400 – 1200 – Estimated 1000 – es e altitude 800 – (m) % it 600- 4 – 00 % at41 200 fp 0 0 0 .. “AU . o .. ,A . 1 0 20 6’0 8 0 100 Victorian Sydney Queensland border border Ranked latitude Figure 2. Scatter plot of altitudes of NSW Sooty Owl sites (n=109) against ranked latitude. Graph prepared by C.J. Chafer The paucity of records on the Central and Southern Tablelands suggests that the species may avoid high altitudes in the south (also Kavanagh & Peake 1993); there is a significant trend of broadening attitudinal tolerance with decreasing latitude (Figure 2: Spearman rank correlation coo 109=0.311, P<0.001). Superimposing the physiographic provinces of Jennings & Mabbutt (1986) on the McAllan & Bruce (1989) botanical regions gives a reasonably good fit: the North Coast and Northern Tablelands fall within the New England -Moreton Uplands; the Central Coast and Tablelands fall within the Macquarie Uplands; and the South Coast and Southern Tablelands fall within the Kosciuskan Uplands. There is a significant difference in the Sooty Owl’s attitudinal distribution within these three physiographic provinces (Kruskal-Wallis test: Hc005,2109:=29.92, P<0.001). The owl’s attitudinal distribution is similar in the Kosciuskan and Macquarie Uplands, but different (i.e. wider attitudinal tolerance) in the New England Uplands (Tukey-type multiple comparisons test: Kosciuskan Uplands vs Macquarie Uplands, q=1.77; New England Uplands vs Kosciuskan Uplands, q=3.11; New England Uplands vs Macquarie Uplands, q=5.65; go 3=2.394). The reasons for this trend may be related to latitudinal trends in: climate (winter temperatures); prey diversity and abundance at high altitudes; survey effort; and/or the attitudinal range of the Owl’s preferred habitat. Furthermore, breaks in the Owl’s distribution (Shoalhaven and Hunter Valleys) coincide with geological boundaries where the infertile Hawkesbury/Shoalhaven Sandstones interrupt the more fertile igneous/metamorphic Kosciuskan Uplands and New England -Moreton Uplands. In the Macquarie Uplands, all Sooty Owl records are from rich sites such as gullies, e.g. where they cut through more fertile shales or coal measures, or where there are igneous intrusions: sites which permit more luxuriant forest growth than that on the sandstone plateaux. The Hunter Valley floor that interrupts the New England -Moreton and Macquarie Uplands also supports unsuitable habitat in the form of rainshadow-induced woodland (I. McAllan pers. comm.). Australian Birds Vol. 28 Supplement S9At a finer scale, there are also significant differences in altitudinal distribution within the 12 Jennings & Mabbutt physiographic regions (Kruskal-Wallis test, Hcoo 7o,)=58.18, P<0.001). A comparison of the mean altitude of Sooty Owl sites within each region, and the number of Owl sites within each region, reveals a strong bias towards escarpment sites <500 m altitude in northern NSW and <300 m in central and southern NSW (Figure 3). Sixty-nine (63%) of 109 NSW Sooty Owl sites fall in just three widely separated regions: the Clarence Fall, Hawkesbury-Shoalhaven Plateaux and Monaro Fall. It is these rugged escarpment regions that tend to be reserved as state forests and national parks, the higher -quality forest on the flatter coastal lowlands having been largely freeholded and cleared. This applies also to the extensively cleared Macleay-Barrington Fall, which partly accounts for the lack of Owl records on the lower North Coast (Figure 1). In NSW Sooty Owls have been recorded at 59 sites in 28+ state forests versus 24 sites in 14 conservation reserves (Appendix 1). This suggests that there is more suitable habitat (i.e. higher -quality forest) and more Owls in state forests than in national parks, i.e. escarpment wood -production forests support major populations of Sooty Owls. IOW 800 Mean altitude (nil 600 T 400 T 200 –T–T T T 0 ME 11 IL CP HP HV I DP MriF AP IE CF CL Kosciuskan Mfficquarto Now England Uplands Upln0s Uplands Physiographic Region / province 20 Number of locations 10 MF 77 IL CP HP IN BP McF AP 7E CF CL Kosaushan Macqusn Now England Uplands 001ends Uplnds Physiographic Region / province Figure 3. Mean altitude (+1 SE) of 109 Sooty Owl sites within the Jennings & Mabbutt (1986) physiographic regions, and the number of Sooty Owl sites within each region. TE = Tenterfield Plateau; AP =Armidale Plateau; BP = Liverpool -Barrington Plateau; CF= Clarence Fall; CL = Clarence Lowlands; McF = Macleay-Barrington Fall; IL = Illawarra Plain; HP = Hawkesbury-Shoalhaven Plateaux; HV = Hunter Valley; CP = Cumberland Plain; TI = Tinderry-Gourock Ranges; MF = Monaro Fall. Graphs prepared by C.J. Chafer SIO Debus: Sooty Owl October 1994DIET AND FORAGING Published diet samples show that in New South Wales the Sooty Owl takes a variety of arboreal and terrestrial mammals of rainforest and sclerophy II forest (Table 1).They also show that the Owl has recently included introduced rats and rabbits in its diet, albeit in a probably limited manner; 20% by number, 21% by biomass of 123 mammalian prey records collated for this paper. The most important mammalian prey species, in terms of numbers taken and the number of sites at which they are recorded as prey, are the Common Ringtail Possum Pseudocheirus peregrinus (24% by number, all sites), Sugar Glider Petaurus breviceps (34% by no., 4 out of 5 sites) and rats Rattus spp. (26% by no., 3 out of 5 sites; Table 1). From the main habits of the mammals (Strahan 1983), one may infer that 61% of 123 captures were made in trees or shrubs, 17% were made on the ground and 22% were made either on the ground or in trees/shrubs. That is, little over half of captures were of exclusively arboreal mammals. By biomass arboreal mammals were of greatest importance (75%), compared with 12% scansorial and 12% terrestrial mammals, and 1 km’ and trees 165+ years old. Although
the Owls were most abundant in old growth, they often occurred in young stands near old growth,
Australian Birds Vol. 28 Supplement S13and some pairs had stands of young and old forest in their home -ranges. Some pairs were in stands
lacking high densities of old live trees, but probably centred on high densities of standing, hollow
dead trees (stags) where there were scattered old live trees.
In more diverse habitat with potential roost sites in gully rainforest (which is excluded
from logging), and where logging operations consist of dispersed coupes with some canopy retention,
Sooty Owls occurred in unlogged and selectively logged wet eucalypt forest with a tall, dense
understorey, on fertile soils. Under these circumstances they favoured mid to late successional
(>60 yr old) and older mixed -age forest with some hollows (NSW South Coast: Davey 1993;
Kavanagh & Peake 1993).
A subsequent study concluded that the Sooty Owl’s distribution was unaffected by logging,
and that it was more frequent in the logged-unlogged mosaic with undisturbed gully refuges than in
extensive unlogged areas (Eden region: Kavanagh & Bamkin in press). However, comparison was
between logged forest on high -quality sites (wet, low elevation) and unlogged forest on lower –
quality sites (dry, high elevation). The effect of logging on Sooty Owls in the high -quality forest
cannot be inferred, beyond the fact that some survived the first half of the first cutting cycle,
because pre -logging densities in the Owl’s preferred habitat are unknown. Nor can such data be
obtained, because most of the highly productive forest at lower elevations has been logged.
Forestry practices may have effects other than the felling of habitat trees. The Sooty Owl
is suspected to be affected by fire burning into its gully refuges (Garnett 1992), although Owls have
persisted (or recolonised?) after fire (Loyn et al. 1986; Hollands 1991). Cool, autumn prescribed
burns at high frequency reduce habitat quality by simplifying the structure and removing resources
used by the Owls’ prey. Native terrestrial and some arboreal mammals (including the Owl’s major
prey) are disadvantaged by this fire regime, whereas introduced species (rats, mice, rabbits) are
advantaged (Catling 1991 and references therein). In practice, prescribed burning schedules in wet
forest may be seldom achieved, both in frequency and in area (R. Kavanagh pers. comm.). The
effect on Sooty Owls may be equivocal, as they include some introduced mammals in their diet
(scansorial Black Rat up to 61% of captures and 70% of mammal prey biomass; from Lundie-
Jenkins 1993). However, in some forested habitats exotics may not compensate fully for declines
in native mammals, if arboreals decline and there are no exotic replacements for these.
The Sooty Owl has shown some ability to persist in forests managed for timber, and some
flexibility in roost sites and prey species. In intensively managed forests, the major issue will be
the shortfall in tree hollows as old trees are lost. A significant factor will be rotation time; the
period between cutting cycles will need to be sufficiently long for regenerating forest to develop
hollows (e.g. Milledge et al. 1991). In areas of integrated logging (woodchipping) where there is
a mosaic of logged and unlogged coupes (e.g. the Eden region: Kavanagh & Peake 1993; Kavanagh
& Bamkin in press), the Owl has survived the first half of the cutting cycle, but the effect of
completion of the first cutting cycle remains to be determined. The maintenance of tree age cohorts,
allowed to develop hollows at intervals into the future, may be critical for the long-term survival of
the Owl. Furthermore, in such presumably long-lived species any change in fecundity associated
with logging regimes (through changes in nest- site or food availability) may take some years to
become apparent and considerable effort to detect.
S14 Debus: Sooty Owl October 1994DISCUSSION
Recent data, in the years leading up to and concurrent with the start of the Sooty Owl
project in northern New South Wales, suggest that the Owl is more widely distributed and more
numerous than hitherto believed. Also, in terms of diet, habitat and other aspects of biology (e.g.
roost sites, occurrence in logged forest) it may be more resilient and less threatened than formerly
believed. Nevertheless, field investigation of these issues is warranted because the Sooty Owl has
major populations in wood -production forests, and those forests may be approaching threshold
levels of old -growth retention or logging intensity for species such as the Sooty Owl. That is,
attrition of resources such as tree hollows, which support the Owl and some of its prey, may render
formerly important habitat marginal and no longer suitable for breeding. Questions need to be
answered on the response of the Owl to logging. Furthermore, it is not simply a question of owl
occurrence in logged versus unlogged forest, but the mosaic of logged/unlogged areas in the landscape
(e.g. proximity to and area of nearby old growth: Milledge et al. 1991), site quality, intensity of
logging and time since logging. There is a danger that results such as those of Kavanagh & Bamkin
(in press) could be taken out of context, and simplistically used to claim that owls “don’t mind”
logging or even benefit from it.
A major question has been whether the Sooty Owl is Australia’s equivalent of the North
American Spotted Owl. In most parts of its range the latter species is dependent on old -growth
(ecologically mature) forest for breeding, roosting and foraging; it avoids young regrowth from
timber -harvesting clearcuts; pairs hold home -ranges of c. 400-4000 ha depending on habitat quality;
its density and reproductive success are higher in high -quality forest scheduled for logging than in
habitat reserves (because high -quality habitat has been freeholded or omitted from reserves); and
Owl populations are on public land because remaining forest on private land is young and simplified
(e.g. Ganey & Balda 1989; Solis & Gutierrez 1990; Carey et al. 1990; Ripple et al. 1991; Bart &
Forsman 1992; Blakesley et al. 1992; Bias & Gutierrez 1992). Work by Carey et al. (1992) and
Mills et al. (1993) has aspects of the Spotted Owl’s ecology, which may
be relevant to the Sooty Owl: (1) Spotted Owl home -range size varies with the number of major
prey species in the diet and with the proportion of old -growth forest in the landscape (prey biomass
being greater in old growth); (2) Owl home ranges are 2-3 times larger in fragmented than in
continuous habitat; (3) the abundance of prey explains the Owl’s requirement for large areas of old
growth; (4) total home -range area used over two or three years is 50% larger than the area used
within one year; (5) the Owl needs forest managed for maximal prey numbers; (6) in unlogged
areas, the Owl prefers to roost and nest in forest with well -developed vertical canopy layering and
large standing dead trees (medium to large stag diameter). The Spotted Owl is also under competition
from an invading congeneric species that is more tolerant of habitat disturbance (the Barred Owl
Strix varia: Shields & King 1990), but the Sooty Owl is apparently under no such pressure. The
sympatric, slightly smaller Masked Owl is sufficiently different for these two Tyto species to co-
exist, with some habitat and prey partitioning (e.g. Schodde & Mason 1980; Debus 1993a; Debus
& Rose, this issue).
Is the Sooty Owl like the Spotted Owl? This review suggests that the Sooty Owl does show
some similarities, particularly in its role as an indicator of diverse and abundant populations of
arboreal mammals. In the forests of NSW it is therefore possibly the most appropriate predatory
bird for forest managers to monitor in order to assess the impact of their activities on wildlife.
There are also some differences between the Spotted and Sooty Owls.
Australian Birds Vol. 28 Supplement S15The Sooty Owl has a greater number of primary prey species (wider prey base), and has
greater flexibility in its breeding season and a greater reproductive potential. However, it is an
obligate hole -nester whereas Spotted can use old stick nests in trees. The Spotted Owl seems more
susceptible to forest management than the Sooty Owl, but this may be because the former is subject
to broadscale clearfelling of habitat whereas the latter is subject to less severe logging practices in
some areas. Perhaps the greatest similarity is in the human social context: the old -growth forest
debate in wealthy western nations that are about to harvest the last of their mature, undisturbed
forests and thereby threaten their specialised fauna, and the contrived “prosperity versus environment”
argument by the timber lobby (but see a benefit -cost analysis of Spotted Owl conservation by
Rubin et al. 1991, in which conservation has a calculated net national benefit).
Finally, a pattern emerging from recent reports of Sooty Owls (Appendix 1) deserves
comment. It is apparent that bird -watchers are “twitching” Sooty Owls at known sites (including
national parks and other reserves, particularly near major urban areas), which may disturb established
pairs if broadcast of taped calls is used frequently. Such repeated visits should only be used for
bona fide research or monitoring of territory occupancy and breeding success, and even then playback
used sparingly. It may be more useful, in terms of knowledge of the Owl’s distribution, habitat
requirements and conservation status, if observers search for the Owl in new areas, particularly
wood -production forests and coastal forests under threat from clearing for development. Such
searches should also include apparently marginal habitat such as dry or logged forest, in order to
determine whether the Owl occurs or breeds in such areas, as even negative reports would be
valuable.
ACKNOWLEDGEMENTS
I thank the RAOU for access to Atlas records, kindly extracted by Lyle Smith, and made by
the following observers: W. Barden, G. Holmes, V. & R. Routley, P. Smith, C.H. Young. I also
thank Alan Morris for advance copies of the 1989-91 FOC bird reports, Penny Olsen for details of
Sooty Owl clutches in egg collections, and E.S. Hoskin for details from the Keith Hindwood Bird
Recording Service. Chris Chafer, Glenn Holmes, Harry Hines, Jean Skinner and Will Osborne
kindly provided records, and Graeme Phipps provided details on the bird held at Taronga Zoo.
Zoltan Enoch provided access to and prepared the skin of the Sooty Owl in the Zoology Museum,
University of New England. Chris Chafer performed the statistical analyses of owl records. He
and Rod Kavanagh provided advance copies of Sooty Owl papers in press and they, along with Drs
Hugh Ford and Harry Recher, Walter Boles and Ian McAllan, commented helpfully on a draft.
Appendix 1
Published and unpublished records of the Sooty Owl in New South Wales, approximately in chronological
order within the regions of McAllan & Bruce (1989). SF = State Forest; NP = National Park; NR =
Nature Reserve; SR = Scenic Reserve. AM = Australian Museum; SAM = South Australian Museum;
Atlas = RAOU atlas record sheets/unusual record forms. Bird Report = NSW FOC annual bird report
(published in Aust. Birds) for a given year; FOC = NSW FOC Newsletter, “unusual records” series by
Morris & Chafer 1990-1992 inclusive (issues 117-133).
Locality Source/comments
North Coast:
Clarence River Type specimen 4.9.1844 (McAllan in prep.)
Richmond River Specimen (AM A.1173) registered 1877.
S16 Debus: Sooty Owl October 1994Kempsey Specimen (AM 0.10924) registered 1898.
Lismore Specimen (AM 0.18279) registered 1912.
Lionsville Roosting bird upper Clarence River 20.10.1918, flushed from bushy tree
(Ramsay1919).
Georges Creek One bird 1928 (de Warren 1928).
Redhead One bird 1972 (Morris 1975).
Border Ranges 1-2 on Tweed Ra., Richmond Ra. and Nightcap Ra. 1973-1983 (Gosper
1986).
Willi Willi NR Roosting bird flushed from rainforest 20.2.78 (M. Dodkin & A. Floyd,
per A.B.Rose).
Bellinger River SF One bird 12.10.79 (G. Holmes/Atlas).
Border Ranges NP (Formerly Wiangarie SF): 1-2 birds at 4 sites 1980-82, 16.1.87 (Bird
Reports; G.Holmes). Three birds Sheepstation Creek -Forest Top early
1990 (H. Hines).
(Formerly Roseberry SF): one bird Oaks Creek 3.9.82 (Bird Report);
recorded Richmond Gap 29.7.88, 4.8.88 (G. Holmes). One bird
Horseshoe Creek 29.1.83 (Bird Report). Recorded Sawpit Creek 6.9.84,
26-27.9.87 (Bird Report; G.Holmes).
Toonumbar SF Recorded April 1980; February, May, August 1981 (Bird Reports; G.
Holmes).
Beaury SF Recorded 14.4.80, 8.10.81, May -June 1983 (Bird Reports); 4.10.84 (G.
Holmes).
Whian Whian SF Recorded Terania Creek January, December 1980, 15.1.81 (Bird
Reports);
Minyon Falls 1.10.84, 8.2.86 (Bird Reports), Nightcap Ra. 1.10.84 (G.
Holmes).
Mt Warning Recorded September -December 1981 (Bird Report).
Candole SF (Bird Report).
Cambridge Plateau Recorded 31.3.84 (Bird Report), one in FR 28.10.88 (H. Hines).
Huonbrook Recorded 9.6.84 (Bird Report).
Yabbra SF Recorded 17.12.84 (south: Bird Report), 31.1.88 (north: G. Holmes).
Rosebank Recorded Coopers Creek 6.4.86 (Bird Report).
Nullum SF Recorded 19.7.86 (Bird Report).
Mebbin SF Recorded 24.1.86, 9.4.87 (G. Holmes).
Byron Bay Juvenile banded 30.6.86, recovered Dungay 49 km NNW 13.7.90 (Anon.
1991).
Nambucca Valley Pair 1989; one road -injured, now at Taronga Zoo (J. Skinner). Found on
Pacific Highway, Nambucca Heads, 15.8.89 (per G. Phipps).
Belmont Two birds Valentine January 1989 (Bird Report).
Copeland Tops One bird 30.3.91 (FOC).
Central Coast:
Woonona Specimen (AM 0.8268) registered 1895.
Sydney “Rare” Georges River and Port Hacking 1898 (Hindwood & McGill
1958).
Manly Specimen (AM 0.13397) registered 1904.
Cambewarra Four records (3 sites) for area including Cambewarra Mtn, Meroo
31.12.27, 15.1.29, 30.6.33, 15.5.38 (A.J. Elliott per E.S. Hoskin, C.J.
Chafer).
Thirroul Observed September 1949 and May 1950 (Gibson 1989).
Australian Birds Vol. 28 Supplement S17Mansfield One bird in gully 3.9.60 (Hoskin et al. 1991).
Wyong SF One bird September 1963 (B. Wallace, J. Thomas per E. Hoskin).
Watagan Mountains One bird 20.6.81 (Bird Report).
Royal NP Pair Lady Carrington Drive 26.9.84 (per E. Hoskin), 14.11.85 and June –
July 1986; 1-2 Bola Creek 1987 (Bird Reports); 4 in park 7.9.91
(Bird Report); one 11.1.92, two 11.8.92 (FOC). Determined as 5 pairs in
Hacking River catchment 1985-92 (Chafer & Anderson 1994).
Grose River Recorded February 1986 (Bird Report); site discussed by Lundie-Jenkins
(1993), i.e. Bowen Mtn on eastern (notwestern) boundary of Blue Mts
NP.
Ourimbah One bird 1973, March -April 1988, June 1990 (O’Brien 1990),12.5.91
(Bird Report).
Ourimbah SF One bird early 1980s (O’Brien 1990).
Strickland SF Pair 5.4.86 (O’Brien 1990); 1-2, 27.10.90, May 1991 (Bird Reports).
Ourimbah One bird Askania Park March 1987 (O’Brien 1990).
Bouddi NP One bird 10.6.87, August 1988, June -July 1990 (O’Brien 1990), 19.1.91
(Bird Report).
Gosford One bird Rumbalara SR 3.12.89, 22.1.90 (O’Brien 1990).
Lisarow One bird Katandra SR August 1988 -June 1990 (O’Brien 1990), 1-2 on
27.10.90 (Bird Report), one January and July 1990 (Bird Report)25.9.92
(FOC).
Erina One bird 3.12.89 (Bird Report).
Jamberoo Pass Recorded 1988-89 (Bird Report 1988; Gibson 1989), 11.12.90 (Bird
Report).
Helensburgh Adult and juvenile 14.11.89, one bird 21.9.91 (Bird Reports) , one
24.5.92(FOC).
Nattai River Four birds 31.3.91 (Bird Report).
Dharug NP One bird Mill Creek 7.9.91 (Bird Report); one in park 4.1.92 (FOC).
Brisbane Water NP One bird Mooney Mooney Dam 24.10.91 (Bird Report); one in park
13.1.92 (FOC).
South Coast:
Pigeon House Mtn One bird 17.10.1926 (A.J. Elliott per C.J. Chafer).
Budjong One bird 14.2.1932 (A.J. Elliott per C.J. Chafer).
Tilba One record 1973/74 (Disney 1979).
Narooma One record 1973/74 (Disney 1979).
Cobargo Road kill 16 km S, July 1975 (Bird Report; AM 0. 45268:
female, 999 g).
Bermagui One bird Murrah SF January, July 1981 (Bird Report; Smith
1984).
Tathra One bird Tanja SF roosting on branch 1-2 m above ground
(26.10.77) and 4 m above ground (3.8.79), in Lillypilly gully rainforest
with Spotted Gum Eucalyptus maculata-Grey Ironbark E. paniculata open
forest on ridges (P. Smith/Atlas); also seen July, September 1981 (Bird
Report).
Batemans Bay One bird Benandurah SF 9.1.83 (Bird Report).
Kioloa SF Three territories identified 1980-89 (Davey 1993).
Eden Recorded 11 sites 1988-89; pairs at five additional sites 1989-90
(Kavanagh 1992; Kavanagh & Peake 1993; 1989 and 1990 Bird
Reports).
S18 Debus: Sooty Owl October 1994Northern Tablelands:
Barrington Three records in 1930s at “Memot” (Hyem 1936). Nine pairs,
some breeding, around “Memot” 1960s- 1970s (Hyem 1979);
sample clutches collected: C/2, 31.1.59 (AM 0.43612); C/2,
11.4.70 (AM 0.61453).
Tenterfield Two pairs breeding McLeods Creek, Girard SF 1966-67 (Fleay
1968); one bird 17.6.75 (Bird Report), 10.6.78 (G. Holmes/Atlas ).
Boonoo Boonoo Two clutches taken: C/2, 5.3.67; C/1, 5.3.69 (Morton Oakley
Collection in SAM, and private egg collection; data per P. Olsen).
Yarrowitch Bred 1977 (C.H. Young/Atlas); pair with fledgling 1988,
breeding pair April 1989 (Hollands 1991).
Gibraltar Range NP Recorded 17.11.80 (Bird Report).
Washpool SF Recorded 1980/81 (W. Osborne).
Mt Boss SF Recorded June, October 1981 (Bird Report).
Gloucester Tops Bred April 1982; recorded 21.4.84 (Bird Reports; Roberts 1983); two
fledglings 26.1.92 (FOC).
New England NP Pairs 13.3.82 and at Point Lookout 1982 (Bird Report).
Dorrigo Road -killed female 20 km W, 17.9.82, 918 g (Bird Report; Zoology
Museum,Univ. New England).
Doyles River SF One bird Cells River area 8.11.89 (H. Hines).
Chaelundi SF One bird 28.11.89 (D. Pugh per H. Hines).
Mt Royal SF Recorded in four catchments 1990 (Shields et al. 1992)
Central Tablelands:
Berrima Undated record (Gibson 1989).13.4.80 (L.E. Smith per C.J. Chafer).
Jenolan Caves Pair bred 1988 and bird(s) using a second cave site 1 km away
(Hollands 1991); one bird 8.1.90 (Bird Report).
Mt Wilson One bird 24.10.92
Southern Tablelands:
Clyde Mountain Recorded winter -spring 1977 (V. & R. Routley/Atlas).
Deua NP Recorded in Marble Arch Caves mid 1980s (?) (Hollands 1991).
Bombala Recorded at one site in region 1988-89 (Kavanagh & Peake
1993).
Tallaganda SF Undated recent record(s) Lowden Forest Park (Anon. 1993).
Australian Birds Vol. 28 Supplement S19Powerful Owl with Common Ringtail Possum Pseudocheirus peregrinus
Sketch: Steve Tredinnick
S20 October 1994THE POWERFUL OWL Ninox strenua IN NEW SOUTH WALES
S.J.S. DEBEIS and C.J. CHAFER2
I
‘Department of Zoology, University ofN ew England, Armidale 2351
2Department of Biological Sciences, University of Wollongong, Northfields Avenue,
Wollongong 2522 (present address: 69 Lake Heights Road, Lake Heights,2502)
SUMMARY’
Records of the Powerful Owl Ninox strenua (n=516) were collated in order to assess the
Owl’s distribution, habitat, biology and perceived status in New South Wales. This provides the
historical context for a field survey of the Owl’s distribution, status and habitat requirements in
northern NSW in 1990-92, in relation to forest management. It is concluded that: (1) the Owl
occurs at all altitudes <1500 m from the coast to the tablelands and western slopes, in open as well
as tall open forest; (2) on the coast its primary prey species is the Common Ringtail Possum
Pseudocheirus peregrinus, and on the tablelands probably the Greater Glider Petauroides volans;
(3) it has a low breeding recruitment rate.
INTRODUCTION
In mid 1988 a project was initiated on the distribution, status and habitat requirements of
the Sooty Owl Tyto tenebricosa and other large forest owls in northern New South Wales. The
rationale for the project, and the role of large owls as “management indicators” and “keystone”
species in wood -production forests, have been discussed elsewhere (Milledge et al 1991; Kavanagh
1991; Debus, this issue).
The Sooty Owl field survey occupied three years 1990-92 inclusive and included the other
large forest owls, the Powerful Owl Ninox strenua and Masked Owl Tyto novaehollandiae, on the
grounds that they may also be affected by logging and clearing. The survey results will be presented
elsewhere.
Data on the Powerful Owl’s diet in NSW are limited to two quantitative studies (Kavanagh
1992; Chafer 1992), and casual records from many locations. Data on diet may be important for
inferring the Owl’s hunting habitat, foraging zone, and the resource requirements (e.g. den sites) of
its prey species (e.g. Kavanagh 1992; Debus & Rose, this issue); diet and food supply are likely to
be important factors in the Owl’s ecology. Data on the Powerful Owl’s breeding biology in NSW
are also limited, but available information may be similarly useful for inferring the Owl’s nesting
requirements and breeding strategy.
METHODS
Data or inferences on the Powerful Owl’s broad distribution, status, habitat and biology
were collated from the literature. Specific sightings of the Owl in New South Wales were collated
from published reports to 1992, museums (Australian Museum, Australian National Wildlife
Collection), the Royal Australasian Ornithologists Union Atlas of Australian Birds (record sheets/
unusual record forms) and Nest Record Scheme, the Australian Bird Banding Scheme, the Keith
Hindwood Bird Recording Service (per E.S. Hoskin), and colleagues’ unpublished notes. Literature
records were obtained from the following sources: Emu; Corella; Australian Bird Watcher;
Australian Birds; Canberra Bird Notes; NSW FOC Newsletter; Cumberland Bird Obervers Club
Newsletter; books, reports and other publications. Some records were reported by more than one
source, therefore care was taken not to double -count records. One record was taken as one bird at
Australian Birds Vol. 28 Supplement S21one locality in one year (i.e. two birds = two records), and nestlings were not counted. Data were
analysed as the number of sites at which the Powerful Owl had been recorded, a “site” being
defined as the area within which a cluster of records can reasonably be assumed to represent a
single occupied Owl territory. Unpublished records are listed in Appendix 1; published records
(Appendix 2) are available from the authors.
Powerful Owl sites were located on topographic maps. They were then sorted into the
botanic zones of Anderson (1961), as adopted by McAllan & Bruce (1989), and within the
physiographic provinces and regions of Jennings & Mabbutt (1986). We used the latter because of
a need for greater understanding of physiographic and biological interactions in order to explain
avian biogeography (e.g. Gentilli 1992). To explain a region’s avifauna, Gentilli used landform,
precipitation and botanical structure. The geomorphological matrix, i.e. the finer scale of
physiographic provinces, should also be considered. This allows greater appreciation ofthe complex
ecological inter -relationships between geology, the climatic patterns that have shaped a region’s
surface and created present soil conditions, and the vegetation communities that developed in response
to the evolving nutrient and moisture base.
Differences between regions or zones and between regional diets, in terms of the frequency
of distributional or prey records in each class, were tested statistically by the log -likelihood ratio
test (G -test; Zar 1984).
HISTORICAL BACKGROUND
The Powerful Owl has traditionally been regarded as rare to uncommon, and restricted to
or most numerous in dense gullies of tall open (wet sclerophyll) forest in hilly or mountainous
areas of the coast and Great Divide (McGill 1960; Fleay 1968; Slater 1970; Macdonald 1973;
Calaby 1976; Schodde & Mason 1980; Slater et a/. 1986; Schodde & Tidemann 1986). Pizzey
(1980), however, included coastal forest, woodland, scrub and exotic pine plantations among its
recorded habitats. There has been a resident, breeding population of Powerful Owls in Sydney
suburban bushland (northern suburbs) since at least the 1950s (per E.S. Hoskin), with specimens
taken earlier from what was then bushland surrounding the outer Sydney suburbs. Inland records
such as that at Gilgandra (McCutcheon 1976) have been regarded as dispersing immatures (Schodde
& Mason 1980), but the Owl has apparently bred in the Pilliga Scrub (Rolls 1979). Blakers et al.
(1984) reported that it occurs also on the inland slopes of the Divide.
In optimal habitat in northern New South Wales, neighbouring pairs of Powerful Owls
have been recorded 3-6 km and often up to 10 km apart (Goddard in Fleay 1968), with home –
ranges estimated at 800-1000+ ha per pair (Schodde & Mason 1980). In NSW, the Owl has been
classified as “uncommon”, defined as an estimated population of 1000 to 10 000 birds in the State
(Morris et al. 1981). In NSW it was recorded in 21 one -degree squares, breeding in two, during the
Atlas of Australian Birds project (Blakers et a/. 1984). The Owl usually roosts on branches of
dense trees in gullies (Schodde & Mason 1980). Rare cases of cave -roosting (Hindwood & McGill
1958; Rose 1993) are probably biologically insignificant, but it is worth reviewing additional
information on the first case, to confirm that it does happen occasionally. A bird was flushed from
a cave [presumably a shallow, sandstone recess or overhang] in daylight in Royal National Park in
1935 by the late K.A. Hindwood, an experienced observer; it was seen well, and feathers and fresh
castings were collected for identification (per E.S. Hoskin). In a possibly analogous situation, in
1980 an immature Owl spent a day roosting on a building at the University of New England,
Armidale (D. Jones pers. comm.). Typical Powerful Owl nest sites have been described as large
vertical hollows in the trunks of trees in gullies, in hilly or mountainous country (Beruldsen 1980).
However, the Owl also uses horizontal or sloping spouts (Schodde & Mason 1980; Hollands 1991).
S22 Debus & Chafer Powerful Owl October 1994
:McAllan & Bruce (1989) attributed a lack of Powerful Owl records partly to a lack of night
observations, and recent work has necessitated further modification of the prevailing view of its
status, distribution and habitat requirements. In western Victoria, Hollands (1991) recorded the
Owl living and breeding in smaller, drier forest and woodland with lower hollows than previously
recorded, and roosting preferentially in pine plantations near eucalypt forest in the non -breeding
season. Hoskin et al. (1991) noted that around Sydney the Owl has become more frequently
recorded over the past ten years. In central coastal New South Wales Chafer (1992) found the Owl
at more locations, in a wider variety of forest types and roost sites, and nesting at lower heights,
than previously recorded. Chafer’s work, and other recent studies in NSW (Davey 1993; Kavanagh
& Peake 1993), Victoria (Traill 1993) and Queensland (Pavey 1993), show that the perceived rarity
of the Owl is largely a problem of observer effort and appropriate survey technique, and that the
Owl occurs and breeds in dry coastal, suburban or inland forest, on flat or undulating terrain.
Recent surveys have produced many Powerful Owl records, with some home- ranges estimated to
cover as little as 400-600 ha per family group in optimal habitat with high prey densities (Davey
1993; Kavanagh & Peake 1993). In a remarkable case, Quinn (1993) recorded two family groups
(each of a pair plus two juveniles) roosting <400 m apart in the same gully. However, the Powerful
Owl is a strictly seasonal breeder with only one nesting attempt per year and a maximum of two
fledglings per attempt (Schodde & Mason 1980). From the number of recorded failures or broods
of one (Fleay 1968; Hyem 1979; Hollands 1991) it apparently has a low recruitment rate, probably
less than one fledgling per territorial pair per year. Chafer (1992) obtained evidence of a Powerful
Owl dispersing several kilometres across open country. This is supported by the case of an immature
Owl at the University of New England (D. Jones pers. comm.): to get there it had to cross several
kilometres of open or lightly wooded country. The Powerful Owl is classified nationally as “rare”
(Garnett 1992), and “vulnerable and rare” in NSW (Schedule 12, Part 2 of the NSW National Parks
and Wildlife Act).
The Powerful Owl’s diet has been considered to consist mainly of arboreal marsupials,
particularly the Greater Glider Petauroides volans, which requires tree hollows as den sites (e.g.
Fleay 1968; Schodde & Mason 1980). Although this may be the case at high altitudes where
Greater Gliders are abundant (James 1980; Kavanagh 1988), in coastal or lowland areas where
other mammals are equally or more abundant, or the Greater Glider is absent, the Owl preferentially
takes Common Ringtail Possums Pseudocheirus peregrinus, Sugar/Squirrel Gliders Petaurus
breviceps/norfokensis and a variety of other mammals and birds (Tilley 1982; Hollands 1991;
Kavanagh 1992; Chafer 1992; Pavey 1992; Traill 1993; Hobson 1993; Rose 1993). In southern
coastal NSW where it specialises on arboreal marsupials and breeds successfully, virtually none of
its prey is restricted to, or even necessarily most numerous in, old -growth forest (Kavanagh 1992;
Chafer 1992).
DISTRIBUTION IN NEW SOUTH WALES
The Powerful Owl occurs in a broad coastal and subcoastal strip in New South Wales
(Figure 1). The records collated (516 from 267 locations) result in no change from its regional
distribution as given by Morris et al. (1981). The broader botanic regions of Anderson (1961) are
therefore used here simply to demonstrate that the Owl occurs at all altitudes <1500 m in eastern
New South Wales, and is not restricted to mountain gullies (coast 61% of sites, tablelands 34%,
slopes 4%, plains <1%: Table 1, Figure 2). There are significantly more coastal than inland sites
(G -test, coast vs tablelands + slopes: G1=13.14, P=0.001).
Australian Birds Vol. 28 Supplement S23153°
150° 151° 152°
149°
141 142° 143° 144′ 145° 146′ 147′ 148°
29°
Al
it
31°
;11
32′
II
34°
35°
37°
Figure 1. Distribution of the Powerful Owl in New South Wales, in ten-minute grids.
There is no significant difference in the distribution of sites between northern, central and
southern botanic zones (G,=1.652, P=0.46). Nor is there any significant difference between coast
and tableland records in tfie northern and southern botanic zones (G7=0.288, P=0.62; G7=0.205,
P=0.60 respectively). However, there is a significant difference in the central botanic zone (more
coastal than tableland sites; Gi=49.363, P<0.001). Similarly, there is a significant difference in the
distribution of sites between the three tableland botanic zones (G2=16.34, P<0.001) and between
coastal botanic zones (G,=11.94, P=0.005). In other words, there are more records for the Central
Coast but fewer for the Central Tablelands than expected, when compared with other coastal and
tableland regions respectively. These differences may partly reflect the lack of surveys in some
regions. The central zone includes the major population centre of Newcastle -Sydney -Wollongong,
which extends inland to the Blue Mountains, yet there are few montane records; most records in the
central zone come from lowland or escarpment forests and sub- montane gully forests.
The western limit of the Owl’s distribution in NSW closely fits the inland boundary of
certain climatic and physiographic zones: the Koppens Cf climatic zone (Gentilli 1986) and the
New England -Moreton, Macquarie and Kosciuskan Uplands physiographic provinces (Jennings &
Mabbutt 1986). These zones are temperate and moist regions producing fertile gullies, gorges and
alluvial plains. This suggests that at a r3ntinental scale, the Powerful Owl is responding to the
S24 Debus & Chafer Powerful Owl October 1994
:effects rainfall, landform and soil fertility have on vegetation structure. At a broad regional scale,
there is a significant difference in the distribution of sites between the New England -Moreton
(n=78), Macquarie (n=116) and Kosciuskan Uplands (n=73) (G ,=11.955, P=0.005; n=267
sufficiently precise locations). At a finer scale, the Powerful Owl has been recorded in 21 of the 25
possible physiographic regions in NSW (Figure 2). The distribution between these regions is
heterogenous (G24=318, P<0.001), with peaks (Figure 2) coinciding with major human population
centres or areas where detailed research on owls has been conducted. The lack of records from the
North-west Slopes (Figures and 2) may reflect a lack of surveys; there should be suitable habitat
1
in the Cunningham Slopes, Nandewar Peaks and Warrumbungle Peaks, and the Owl might be
expected there.
Table
1
Number of sites at which the Powerful Owl has been recorded in NSW, within the regions defined by
McAllan & Bruce (1989). For clusters of records, a “site” encompasses those assumed to refer to a
single occupied Owl territory.
Region N sites
North Coast 46 17
Central Coast 76 29
South Coast 41 15
Northern Tablelands 41 15
Central Tablelands 13 5
Southern Tablelands 37 14
North-west Slopes 2 <I
Central -west Slopes 8 3
South-west Slopes 2 <1
North-west Plains <I
1
Total 267
The foregoing analyses may have been biased by greater observer density and effort around
major cities; the work of Fleay (1968) and Hyem (1979) on the Northern Tablelands; and recent
surveys on the South Coast and Southern Tablelands (Kavanagh 1992; Davey 1993; Kavanagh &
Peake 1993). Nevertheless, a physiographic explanation is also possible for the pattern of mostly
lowland Owl records in the central zone. This zone (Central Coast and Central Tablelands),
corresponding with the Hawkesbury-Shoalhaven Plateaux physiographic region, is dominated by
massive sandstone uplifts, yielding poor -quality soils. It is heavily dissected, cutting through richer
volcanic and carbonaceous deposits that produce more fertile soils and dense forests (see Fairley &
Moore 1989). Therefore, within this zone Powerful Owls may be expected to favour the relatively
higher -nutrient sites at lower altitudes. It is not clear why there should be so few records for the
adjacent Bathurst Tablelands; perhaps this reflects a lack of surveys there.
In NSW the Powerful Owl has been recorded at 73 sites in 46 state forests, and 52 sites in
32 conservation reserves (Appendices and 2). This serves to illustrate that it has significant
1
populations in wood -production forests. Many of the sites in conservation reserves (and about half
of these reserves) are on the infertile Hawkesbury-Shoalhaven Plateaux (Figure 2), in poorer -quality
habitat unwanted for wood production. In other words, there is little high -quality Owl habitat
Australian Birds Vol. 28 Supplement S25specifically reserved for conservation. However, conservation reserves have been poorly surveyed
for owls relative to state forests, and there are ameliorative effects from conservation efforts within

state forests.

80
Number
60 –
of
40
locations
20 –
0 ., 1 1 r 1,
NC NT MIS NVvP CC CT CWS SC ST SWS
(northern zone) (central zone) (southern zone)
Botanic Region (zone)
50
40
Number
30
of
20
locations
10
7 R nri
0 I , , ,
(New England Uplands) (Macquarie Uplands) (Kosciuskan Uplands)
Physiographic Region (Province)
Figure 2. Number of NSW sites (total 267) with Powerful Owl records, within the botanic regions of
Anderson (1961) and the physiographic regions of Jennings & Mabbutt (1986). For the latter, ML =
Moreton Lowland; CS = Cunningham Slopes; TP = Tenterfield Plateau; CF = Clarence Fall; CL =
Clarence Lowlands; NP = Nandewar Peaks; GL = Gunnedah Lowlands; AP = Armidale Plateau; LBP =
Liverpool -Barrington Plateaux; MBF = Macleay-Barrington Fall; MS = Mitchell Slopes; W =
Warrum bungle Peaks; NIP = Merriwa Plateau; HV = Hunter Valley; GC = Goulburn Corridor; BT =
Bathurst Tablelands; HSP = Hawkesbury-Shoalhaven Plateaux; CIIL = Cumberland Plain; IP = Illawarra
Plain; HS = Hume Slopes; WS = Werriwa Tablelands; AA = Australian Alps; TR = Tinderry-Gourock
Ranges; MF = Monaro Fall; MT = Monaro Tableland.
S26 Debus & Chafer Powerful Owl October 1994
:HABITAT AND ROOST SITES
For 27 locations from which the Powerful Owl’s habitat has been recorded or confidently
inferred (at the detection site, i.e. within c. 1-10 ha) in New South Wales, closed forest was the
major structural formation at two sites (7%), tall open forest at 14 (52%), open forest at 10 (37%)
and woodland at one (4%; sources in Tables 2-4, Appendices and 2). These, together with the
1
many inland and coastal sites from which the Owl has been recorded, show that the Owl is not
restricted to tall open forest in mountain gullies, but does occur in the drier open forests as well.
Although tall open and open forest appear to be its most important habitat types, it also uses woodland
and riparian habitats.
In New South Wales the Powerful Owl roosts in a variety of sites from dense canopy and
substorey trees within rainforest (closed forest) and open forest, often in gullies, to canopy trees in
woodland (Table 2). Commonly recorded roost sites in coastal areas are Red Turpentine Syncarpia
glomuliftra in tall open forest, and Black She -oak Allocasuarina littoralis in open forest. These
and other commonly used roost trees have dense crowns; this suggests a requirement for seclusion,
with some local preference for available species that meet this requirement. The Powerful Owl has
been characterised as shy and retiring (e.g. Fleay 1968), but some roost sites have been within 300-
500 m of popular picnic areas (Royal National Park; also Bass Point: Chafer 1992) or even sometimes
much closer (Hollands 1991; R. Kavanagh pers. comm.). It is possible that records of roosting
Owls are biased by the greater visibility of Owls that perch in open trees, while clutching large prey
(e.g. Fletcher & Reckord 1989).
Table 2
Roost trees of the Powerful Owl in New South Wales: number of sites at which each tree species has been
recorded as a roost. For tree habit, C = canopy species, S = substorey. Sources: references in Tables 3,
4; Appendices 1, 2.
Tree species Habit N sites
Acacia sp. S 2
Acmena smithii C 2
Allocasuarina littoralis S 5
Angophora floribunda C 2
Ceratopetalum apetalum C 4
Eucalyptus camaldulensis C
1
E. dives C 1
E. fastigata C 1
E. paniculata C 1
Eucalyptus sp. C 3
Exocarpus cupressiformis S 1
Ficus obliqua C
1
Ficus sp. C 2
Melaleuca styphelioides S 1
Nothofagus moorei C
1
Podocarpus elatus C
1
Schizomeria ovata C
1
Syncarpia glomulifera C 6
Tristaniopsis laurina S 1
Australian Birds Vol. 28 Supplement S27DIET AND FORAGING
In New South Wales the Powerful Owl takes a range of vertebrates from forest, woodland
and possibly along boundaries with more open country (Table 3, this paper; also Kavanagh 1992,
Chafer 1992). The dietary sources analysed for this paper were casual records, heavily biased
towards daylight records of Owls holding large prey at roosts and large, intact items in nests, with
little pellet analysis. Some caution is therefore required in interpreting the data. Nevertheless two
large arboreal mammals, the Greater Glider and Common Ringtail Possum, were the two most
frequent prey items among casual observations (Table 3). Ignoring the insects (2% by number and
negligible biomass), most captures were mammals (88% by number, 96% by biomass). Of these,
we infer that 85% were arboreal, 7% terrestrial and 8% from either trees or the ground (probably
mostly in trees in the case of the Common Brushtail Possum Trichosurus vulpecula). Furthermore,
most of the birds (10% by number, c. 4% by biomass) were probably taken at night at their tree
roosts; only the Tawny Frogmouth Podargus strigoides was probably taken while it was active.
Observed prey mammals were 80% arboreal, 14% scansorial and 6% terrestrial by biomass. Although
large arboreal mammals may be slightly over -represented, these results are similar to two quantitative
studies for southern NSW (Kavanagh 1992; Chafer 1992; G2=3.053, P=0.222). In the latter study,
86% of vertebrate prey were mammals and 14% birds (88 and 12% by biomass); of the mammals
89% of captures were arboreal (88% by biomass), 8% scansorial (8% by biomass) and 2% terrestrial
(3% by biomass; calculated from Chafer 1992). All these data for NSW, as for other states (see
above), show that the Powerful Owl is dependent on several staple foods (medium and large arboreal
marsupials) whose relative importance varies regionally, although it also takes other prey
opportunistically. For instance, the Owl’s diet is predominantly the Sugar Glider at Culburra
(Chafer 1992). The Owl may take whichever medium or large arboreal mammal is the most available
at a given locality, supplemented by a range of other small to medium-sized, mainly arboreal
vertebrates.
The two quantitative studies from southern NSW (Table 3 of Kavanagh 1992; Table I of
Chafer 1992) illustrate regional differences in the Powerful Owl’s diet, even over short distances of
coastline. Both diets contain a high proportion of Common Ringtail Possums, but they differ in the
relative contribution of other animals. Owls in the Illawarra region take a relatively greater proportion
of Sugar Gliders and Black Rats Rattus rattus, compared with Owls in the Eden region which take
a greater proportion of Ringtails (Figure 3: relative % dissimilarity index, from Ramsey & Marsh
1984). This suggests that the Powerful Owl’s diet varies regionally according to local availability
of prey species. Also, in heavily disturbed areas it may be forced to take smaller and some exotic
prey, but nevertheless breeds successfully on such a diet (Chafer 1992). Elsewhere, the Owl also
takes small prey when larger species are scarce (Van Dyck & Gibbons 1980).
S28 Debus & Chafer Powerful Owl October 1994
:Table 3
Diet of the Powerful Owl in New South Wales (including the ACT), excluding quantitative studies by
Kavanagh(1992) andChafer (1992): minimum number of prey individuals from observations and
samples. Mean or median adult mammal weights from Strahan (1983); juveniles assumed to be half
adult weight. Habits of mammals: A = arboreal, S = scansorial, T = terrestrial. For N prey, I = lowland
(coast/ slopes/ plains), h = highland (tableland) records. Sources: Gould (1843); Jackson (1907); Ramsay
(1919); Hindwood & McGill (1958 and unpubl. notes); Fleay (1968); McCutcheon (1976); Hyem (1979);
Ross (1986); Kavanagh (1988); Fletcher & Reckord (1989); Swift (1991); Sansom (1991); Rose (1993);
NSW FOC annual bird reports in Aust. Birds; COG annual bird reports in Canberra Bird Notes; D.
Read; A.R. Davis; M. Anderson; CJC; SJSD (unpubl. casual obs.).
Species Weight Habit N No. sites
(g)
1
Common Ringtail Possum
Pseudocheirus peregrinus 900 A 13a 7 12b
Greater Glider Petauroides volans 1300 A 3 44 12c
Yellow -bellied Glider Petaurus australis 575 A 3 2
Sugar Glider Petaurus breviceps 128 A
1 1
Common Brushtail Possum
Trichosurus vulpecula 2875 S 6a 4
Koala Phascolarctos cinereus (juv.) 2000? A
1 1
Bettong/potoroo Bettongia/Potorous sp. 1400 T I 1
Red -necked Pademelon (juv.?)
Thylogale thetis 2000? T
1 1
Grey -headed Flying -fox
Pteropus poliocephalus 677 A 2 2
Bush Rat Rattus fuscipes 125 T 3 2
Black Rat Rattus rattus 280 S I 1
Hare Lepus capensis (juv.?) 2000 T
1 1
Total mammals 30 57
Tawny Frogmouth Podargus strigoides
1 1
White -winged Chough
Corcorax melanorhamphos 3+
1
Australian Magpie Gymnorhina tibicen I 1
Pied Currawong Strepera graculina
1 1
Australian Raven Corvus coronoides 1 1
Bird sp. 3 3
Total birds 10
Insects (beetles) 2+ 2
Total sites sampled 30
a Two juveniles b 10 coastal, 2 tableland c 3 coastal, 9 tableland
Australian Birds Vol. 28 Supplement S29Prey Taxon
Sugar Glider
Black Rat
Fruit Bat
Feral Cat
Bush Rat Eden Illawarra
Rabbit region region
Insects
Birds
Yellow -bellied Glider
Greater Glider
Brushtail possum
Ringtail Possum
25 20 15 10 5 0 5 10 15 20 25
% DIS
Figure 3. Dietary dissimilarity (relative percentage dissimilarity, %DIS) of the Powerful Owl in two
areas of southern coastal NSW. Quantitative data from the Eden region (Table 3 of Kavanagh 1992:
4 sites, 112 prey items) and Illawarra region (Table 1 of Chafer 1992: 2 sites, 107 prey items). The
closer the values to zero, the less difference in relative utilisation between the two regional diets
(computed by the method of Ramsey & Marsh 1984).
Further analysis of the casual records (Table 3) suggests attitudinal variation in the Powerful
Owl’s diet, with Greater Glider and Common Ringtail differentially dominant in lowland versus
highland zones. Highland records consist entirely of mammals, of which Greater Gliders contribute
77% and Common Ringtails 12% by number. Lowland (mainly coastal) records consist of 71%
mammals, 24% birds and 5% insects, of which Common Ringtails contribute 31% and Greater
Gliders 7%. Previous detailed studies (Kavanagh 1992; Chafer 1992) were from lowland sites,
thus precluding an accurate coastal/montane comparison, and further data (including pellet analysis)
from highland sites are required. Recent data confirm that Greater Gliders are indeed important
prey in some highland areas (R. Kavanagh pers. comm.). The Owl does take some Ringtails and
Sugar Gliders at highland sites (James 1980). Nevertheless, Table 3 suggests that the Powerful
Owl’s diet is more diverse in lowland areas. This may be related to faunal diversity and abundance
in highland versus lowland forests, i.e. Greater Gliders are abundant in highland forests and are
probably easy to catch. In coastal NSW the Owl’s major prey, the Common Ringtail Possum, is
not dependent on tree hollows but the reverse is true on the tablelands: the Greater Glider requires
hollows and is most abundant in old -growth (mature, undisturbed) forest (e.g. Strahan 1983,
Kavanagh & Bamkin in press). This may have implications for forest management.
Three (possibly up to nine) of 516 Powerful Owl records (1-2%) were of road -killed or
road -injured birds. This is similar to 1% of 226 Sooty Owl records (Debus, this issue), but contrasts
with the Masked Owl, for which 20% of 197 records were road casualties, mostly in or near coastal
forests (Debus & Rose, this issue). Furthermore, Powerful Owls are almost never seen by random
spotlight -driving along forest roads, unlike Masked Owls which can be seen this way, albeit
S30 Debus & Chafer : Powerful Owl October 1994infrequently (pers. obs.). This suggests that the Powerful Owl is much less inclined to use low
perches beside breaks in ground cover, and is consistent with the view that the Powerful Owl, like
the Sooty Owl, is more active in the tree canopy and takes fewer terrestrial prey than the Masked
Owl (e.g. Schodde & Mason 1980).
BREEDING
Breeding data for the Powerful Owl in New South Wales are heavily biased by the number
of attempts not detected until the fledging stage; conclusions on those nests found at the egg stage
are affected by the large number of nests robbed of eggs or young by humans (Table 4). Recorded
nests have been in tall open (12) and open forest (5), in live eucalypts with hollow entrances 9-37
m above ground (mean 23 m, n=8). These heights suggest that nest trees used are typically emergents,
often the largest within a stand and probably among the oldest within a forest patch. Events listed
in Table 4, together with nesting chronology, incubation and nestling periods given by Schodde &
Mason (1980), indicate laying in late autumn to mid winter, with laying starting slightly earlier in
northern NSW (mid autumn, exceptionally in late February). The modal clutch size is two (C/1 x
4, C/2 x 14, mean 1.8). Within a year, a replacement clutch seems possible only if failure occurs
early in the egg stage; pairs that fail often abandon the attempt until the next year (Fleay 1968;
Hollands 1991). For successful nests the brood size at fledging is one or two, with almost equal
frequency (B/1 x 11, B/2 x 10; mean 1.5). Counting only those nests found before the fledging
stage, nine young (0.8 young per attempt) were raised from 11 attempts for which the outcome was
known (including felled nest trees as failures, but excluding nests robbed by collectors). This may
be an overestimate of productivity, as nest failures are common owing to infertility, chick death
(e.g. air -sac mite: Fleay 1968), sensitivity of the owls to human intrusion, and pairs foregoing
breeding in some years (Fleay 1968; Hyem 1979; Hollands 1991; Appendix 1, this paper). Even if
0.8 young per attempt is a reasonably accurate figure, it is lower than that for Masked and Sooty
Owls (1.2 and 0.9 young/attempt: Debus 1993a; this issue), low by raptorial standards and comparable
with the productivity of eagles (e.g. Marchant & Higgins 1993). Powerful Owl productivity in
Victoria was between 0.4 and 0.5 young per pair per year (5 pairs over 5 years, from Hollands
1991). The Powerful Owl was formerly persecuted heavily by egg collectors, particularly in the
Tenterfield region of NSW. Furthermore, the post -fledging dependence period is long, lasting up
to and possibly inhibiting breeding in the next season (Hollands 1991; Table 4, this paper; SJSD
pers. obs.). During this time juveniles are apparently subject to heavy first -year mortality (injury,
air- sac mite, disease/starvation: Fleay 1968; Rose 1993; Table 4/Appendix 1, this paper). Given
the Owl’s strictly seasonal breeding, single attempt per year and low recruitment, pairs probably
take many years to achieve self-perpetuating fecundity (a mean of two descendants of breeding age
per pair). Powerful Owls (both sexes) reach sexual maturity at two years old, and can breed at this
age in captivity (Fleay 1968). However, age at first breeding may be greater than this in the wild,
particularly for males which must acquire sufficient hunting experience to provision a mate and
offspring efficiently.
Recent records reveal that breeding Powerful Owls habituate to passive human presence,
and are tolerant of low-level disturbance near the nest tree. Pairs have bred successfully in an urban
forest picnic area (Pavey 1993), a disturbed forest park (Quinn 1993), and in a caravan park where
the nest hollow was directly over a tent (McNabb 1994).
Australian Birds Vol. 28 Supplement S31Table 4
Breeding parameters of the Powerful Owl in New South Wales (including the ACT). North = north of
Hunter Valley, south = south of Hunter Valley. TOF = tall open forest, OF = open forest. E =
Eucalyptus. Height = height of hollow entrance above ground. Sources: 1 = Ramsay (1919); 2 = P.
Olsen (see Appendix 1); 3 = Hyem (1979); 4 = Fleay (1968); 5 = J. Courtney; 6 = Ross (1986); 7 =
Fletcher & Reckord (1989); 8 = Olsen (1987); 9 = Chafer (1992); 10 = E.S. Hoskin; 11 = R. Webb; 12 =
Rose (1993); 13 = NSW FOC annual bird reports in Aust Birds; 14 = Routley (1980). C/1= clutch of 1,
etc.
Habitat Nest tree sp. Height Month Stage Clutch/brood Source
(m) size (n)
North:
TOF “grey gum” 24 Sept ? ? 1
? ? ? May eggsa C/2 x 3 2
? ? ? June eggsa C/1 x 2,
C/2 x 5 2
TOF eucalypt ? June eggsb C/2 3
TOF eucalypt 21 June eggsb C/2 3,4
TOF ? 37 Feb eggs C/2 4
TOF E. grandis 37 July chicksa B/2 4
TOF E. microcorys 24 July chicksa B/2 4
TOF ? ? Nov fledglings B/2 5
South:
? ? ? Jan fledglings B/2 2
OF ? ? Nov fledglingc B/1 2
TOF E. viminalis 21 July hatchlingd B/1 6
? ? ? Oct fledgling B/2 7
Dec post -fledge B/1 7
OF E. punctata 10 Aug fledglings B/2 8,9
OF E. pilularis 9 Dec fledglings B/2 9
Jan fledglings B/2 9
TOF ? ? Nov fledglings B/2 9
OF E. sclerophylla 10 Sept fledglings B/2 9
TOF eucalypt 29 Nov fledgling B/1 9
? ? ? Oct -Nov fledgling B/1 10
OF ? ? July nestlinge B/1 11
? ? ? July nestlingse B/2 11
? ? ? Aug fledgling( ? 11
? ? ? Dec fledglings ? 12
? ? ? Jan fledglings B/2 12
? ? ? Oct -Jan fledglings B/1 x 4,
B/2 x 1 13
? ? ? Jan -Mar,
Apr, post -fledge B/1 x 3 13
Jan -Jun
TOF ? ? fledgling B/1 14
arobbed binfertile cspecimen (road kill?) ddead enest tree felled, young
rescued (found injured g found sick, died
S32 Debus & Chafer : Powerful Owl October 1994THE IMPACT OF FORESTRY
The role of large forest owls as “management indicators” or “keystone” species has been
reviewed by Milledge et aL (1991) and Kavanagh (1991): owl populations may reflect the ecological
integrity of wood -production forests, and management of such forests for the owls may assist in
conservation of other hollow -dependent vertebrates and indeed other forest- dependent flora and
fauna. The trophic flow -down effect from intentional or unintentional removal of principal predators
may result in a dramatic reduction of faunal species diversity and simplified primary production
(e.g. Roughgarden 1989). This is related to competition between herbivores for niche space.
Predation maintains diversity through selective culling; predator removal may allow r -selected
herbivores to out -compete other species and thereby dominate a habitat, selectively overgrazing
some plant species in the process. Large owls contribute to the stability of forest ecosystems
(Davey 1993).
The problem of conserving these owls in forests intensively managed for timber has been
discussed by Brouwer & Garnett (1990) and Garnett (1992). Given that about 20% of the tall open
forest and 50% of the open forest in NSW has been cleared (from Lunney 1991), populations of the
Powerful Owl may have declined by up to 50% through habitat loss; its remaining habitat is
fragmented and subjected to logging, grazing, burning etc. However, Owls may be more abundant
in high site -quality (tall open forest) than in lower site -quality (open) forest, meaning that populations
may have declined by somewhat less than 50%. The concern is whether it can survive in forest that
is converted from old growth to regrowth or plantations (exotic or native), because intensive forestry
practices remove many hollows which are potential nest sites for the Owls or den sites for their
prey. Intensive logging also causes a decline in arboreal hollow -dependent marsupials, particularly
the Greater Glider (e.g. Kavanagh 1991 and references therein; Kavanagh & Bamkin in press).
Evidence reviewed in this paper suggests that the Owl persists in a variety of disturbed environments
where the tree cover is retained or regenerates; there is little evidence that it is adversely affected by
habitat modification other than clearfelling and conversion to an open landscape.
The Powerful Owl has not been suggested as an Australian equivalent of the North American
Spotted Owl Strix occidentalis as a conservation symbol, nor has it generated the same level of
concern as the Sooty Owl (see Sooty Owl review, this issue). This is consistent with the fact that
the Powerful Owl requires hollows only for nesting, not roosting, and that it is an opportunistic and
generalised predator, some of whose prey do not require tree hollows. However, there has been
some concern that it may be adversely affected by the cumulative loss of old -growth elements in its
habitat, both through loss of nest sites and reduction of prey densities and diversity (Garnett 1992).
It is said to be affected by conversion of forest to pine or native tree plantations (Blakers et al.
1984), but some pairs choose to roost in pine plantations near forest (e.g. Hollands 1991). It
persists in forests that have been selectively logged for over a century (Garnett 1992). Veerman
(1986) suggested that a predominance of Greater Glider in the Owl’s diet indicates optimal habitat,
whereas a predominance of Common Ringtail Possum in its diet indicates a shortage of suitable
habitat. Against such an interpretation is the fact that Powerful Owls can breed successfully on a
diet mostly of Common Ringtails or Sugar Gliders and virtually no Greater Gliders (Van Dyck &
Gibbons 1980; Tilley 1982; Hollands 1991; Kavanagh 1992; Chafer 1992; Pavey 1992, 1993;
Traill 1993). The Powerful Owl appears to have somewhat broader and more generalised habitat
requirements than the Sooty Owl (Davey 1993; Kavanagh & Peake 1993). Kavanagh & Bamkin
(in press) reported the Powerful Owl at equal frequencies in extensive unlogged forest versus a
logged/unlogged mosaic with dispersed coupes and large gully reserves; its major prey species in
the region (Common Ringtail Possum) was not disadvantaged by logging (Kavanagh & Bamkin in
press).
Australian Birds Vol. 28 Supplement S33Forestry practices may have effects other than the felling of habitat trees. The Powerful
Owl is said to be affected by bushfires, which reduce prey numbers (Blakers et al. 1984). Cool,
autumn prescribed burns at high frequency reduce habitat quality by simplifying the structure and
removing resources used by the Owls’ prey; most of its major prey species are disadvantaged by
such a fire regime (Catling 1991). In practice, burning schedules may be seldom achieved in
frequency or in area, with gullies generally remaining unaffected by burning (R. Kavanagh pers.
comm.).
The Powerful Owl has shown some ability to persist in forests managed for timber, and
shows some flexibility in prey species. In intensively managed forests, the major issue will be the
shortfall in tree hollows as old trees are lost. Although foresters maintain that they never cut all the
trees in a coupe, and that habitat trees will always develop, there is increasing pressure on forests
leading to possible overcutting. A significant factor will be rotation time: the period between
cutting cycles will need to be sufficiently long for regenerating forest to develop hollows (e.g.
Milledge et al. 1991). This consideration is both for the benefit of existing Owl territories, so they
have a supply of nest sites in perpetuity, and future potential territories as cut -over forests (e.g. in
coastal NSW) mature. In areas of integrated logging (woodchipping) where there is a mosaic of
logged and unlogged coupes (e.g. the Eden region: Kavanagh & Peake 1993, Kavanagh & Bamkin
in press), the Owl has survived the first half of the cutting cycle, but the effect of completion of the
first cutting cycle remains to be determined. In the future, adequate provision for habitat trees and
gully reserves of unlogged forest may be critical, including the provision of age cohorts of trees
allowed to develop hollows at intervals into the future. New foraging space for dispersing young
Owls will be limited by the total area of suitable habitat available.
DISCUSSION
This review confirms a growing realisation that the Powerful Owl is more numerous, flexible
and resilient, with a wider habitat, altitudinal and dietary tolerance, than formerly believed. As in
Queensland (Pavey 1993), it is probably “uncommon” in New South Wales (as assessed by Morris
et al. 1981). Nevertheless it may be susceptible to local declines in prey abundance in wood –
production forests during periods of logging, particularly on the tablelands where the Greater Glider
may be its major prey. The Owl has specialised breeding requirements, and it is apparently a long-
lived, k -selected species with a low annual recruitment. It may therefore be vulnerable to additional
human pressures on its reproductive output, through declines in food supply or nest availability.
Furthermore, habitat fragmentation may cause problems for young Owls dispersing and finding
mates. These effects may take many years to become apparent, may be difficult to detect and
quantify, and recovery may take a very long time. The Owl has significant populations in wood –
production forests. Therefore, it warrants recognition as a species whose conservation status is of
concern nationally (Garnett 1992) and in NSW (National Parks & Wildlife Act, Schedule 12 Part
2). Surveys of its occurrence in relation to logging in NSW state forests are necessary, and are now
being undertaken widely; there is a need for data also from conservation reserves. Monitoring of
its long-term fecundity in relation to forest management (logging, fire) is also required. Indeed, we
suggest that experimental before -and -after, control -versus -impact comparisons (e.g. Green 1993)
should be conducted in future logged forests, on Owls and their prey and using present survey
techniques. Results will take time, perhaps 5-10 years, but may be a useful supplement to “snapshot”
comparisons, radio -tracking attempts and detailed studies of the Owl’s ecology (Kavanagh 1992,
Kavanagh & Bamkin in press; Kavanagh in prep.). A major impediment to detailed study of
habitat use is the difficulty of catching the birds for radio- tracking (Kavanagh 1992), hence the
need for emphasis on other approaches.
S34 Debus & Chafer Powerful Owl October 1994
:These last points require amplification. The Owl may well occur in logged and unlogged
forests, even with seemingly equal frequency, but critical factors may be logging intensity, time
since logging and site quality. The Owl and some of its prey (gliders) may reach their highest
densities in forests containing old -growth communities (cf. Scotts 1991). Furthermore, Owl presence
per se may not be as reliable an indicator as “performance” measures such as breeding density and
productivity, home -range size and prey density. Owls may subsist in logged forests, but can they
obtain enough food for egg production or successful raising of fledglings? Forest managers cannot
be content simply with the knowledge that Powerful Owls occur in logged forests, but must consider
the long-term availability of the Owl’s resources (nest sites; prey populations and their resource
requirements). Corridors for dispersal of young Owls may also need to be considered. It is recognised
that surveys for presence/absence are a valid component of the overall approach, and that all current
owl studies are of necessity interim in nature.
The Powerful Owl is not the reclusive species, confined to mountain forests, that it was
once thought to be. It inhabits a range of environments and is well distributed throughout eastern
NSW. There is some evidence that different prey species are dominant features of the Owl’s diet at
different spatial scales (e.g. Common Ringtail on the coast, possibly Greater Glider on the tablelands,
but Common Ringtail or Sugar Glider at specific coastal sites). This is potentially important for
areas such as wood -production forests, where conservation measures can be incorporated into
management plans. Besides the necessity for suitable tree -hollows for nesting, there may be regional
differences in roost -site preferences and other resource requirements, leading to regional differences
in Owl density and home -range size.
Finally, a pattern emerging from recent reports of Powerful Owls (Appendices 1 and 2)
deserves comment. It is apparent that bird -watchers are “twitching” Powerful Owls at known sites
(including national parks and other reserves, particularly near major urban areas). This may do
little harm if nesting areas are not found or visited until after young have fledged. However, it may
disturb established pairs if imitations or broadcast of taped calls are used frequently. Playback
should only be used sparingly for bona fide research or monitoring of territory occupancy and
breeding success. It may be more useful, in terms of knowledge of the Owl’s distribution, habitat
requirements and conservation status, if observers search for the Owl in other areas, particularly in
wood -production forests, unsurveyed conservation reserves, “new” suburban bushland sites and in
drier forests on the western slopes. Furthermore, data are required on the annual number of young
fledged per territorial pair or nesting attempt, which necessitates the finding of nests before the
fledging stage (egg or nestling stage, late autumn to winter); observers should therefore be alert to
potentially adverse effects of their presence near nests at the egg or chick stage. Also, observers
should be wary of attacks by adults defending the nest or fledglings (e.g. McNabb 1987; Gibbons
1989; Hollands 1991; Chafer 1992; R. Kavanagh pers. comm.).
ACKNOWLEDGEMENTS
We thank the RAOU for access to Atlas records, kindly extracted by Lyle Smith, and
submitted by the following observers: J. Armstrong, D. Barton, D. Bates, R.M. Cooper, F. Creer,
R. Cox, C. Davey, M. Eldridge, H. Dowd, D. Geering, A. Gibson, B. & H. Haigh, J. Hobbs, D.
Larkins, P. Lipscombe, E. Lisser, H. Mawdsley, D. Milledge, T. Moore, E.G. Reynolds, A.B.
Rose, V. & R. Routley, L.E. Smith, P. Smith, G. Stevens, C.H. Young. We also thank C. Brandis,
J. Courtney, A.R. Davis, J.D. Gibson, H.B. Hines, G. Holmes, D. Jones, L. Klumpes, R. Kooyman,
W. Osborne and E.S. Hoskin (Keith Hindwood Bird Recording Service) for unpublished sightings;
and Belinda Dettman for data in the Australian Bird and Bat Banding Scheme. Dr Penny Olsen
kindly provided data from egg collections and the RAOU nest record cards studied by her, and data
on specimens from the Australian National Wildlife Collection. Graeme Phipps and Rick Webb
Australian Birds Vol. 28 Supplement S35provided information on injured wild owls received by Taronga Zoo and Featherdale Wildlife
Park, respectively. Drs Hugh Ford, Harry Recher and Rod Kavanagh commented helpfully on a
draft, as did Peter Roberts and a referee.
Appendix
1
Unpublished records of the Powerful Owl in New South Wales, approximately in chronological
order within regions defined by McAllan & Bruce (1989). AM = Australian Museum; ANWC
= Australian National Wildlife Collection, CSIRO, Canberra; Atlas = record sheets / unusual
record forms for specific records in Blakers et aL (1984). NP = national park; NR = nature
reserve; SF = state forest.
Locality Source/comments
North Coast:
Richmond River Specimen (AM A.1172), registered 1877.
Clarence River Specimen (AM A.1597), registered 1878.
Dungog Recorded between 1959 and 1961 (J. Hobbs/Atlas).
Wauchope Recorded in region 1975/76 (D. Geering/Atlas).
Mt Nullum Recorded between Sept. and Dec. 1977 (M. Eldridge/Atlas).
Middle Brother SF Recorded between Mar. and Aug. 1978 (D. Milledge/Atlas).
Wollombi Recorded 24-25.3.78 (D. Bates/Atlas).
Coutts Crossing Recorded 1979/80 (H. Mawdsley/Atlas).
Iluka NR One bird 24.4.80 (A. Gibson/Atlas).
Woko NP One bird 3.6.80 (A.B. Rose/Atlas).
Old Bar Recorded winter and spring 1980 (R. Cox/Atlas).
Grevillia Gorge Recorded Mar. 1981 (G. Holmes).
Dorrigo NP Bird flew across road at night 29.4.84 (CJC).
Mt Lindesay SF Recorded 11.4.89 (G. Holmes).
Dalmorton SF One bird 28.10.89 (H. Hines).
Nullum SF Juvenile circa 1989 (R. Kooyman).
Coffs Harbour Adult banded by D. Page, Coffs Ck 12.6.91 (per B.Dettman)
Specimen (ANWC 44117) within km of city centre, 16.6.91; adult
1
male, 995 g.
Central Coast:
Campbelltown Specimen (AM A.8189), registered 1880.
Smithfield Specimens (AM 0.6202, 12136), registered 1893, 1901.
Macquarie Fields Specimen (AM 0.18275), registered 1912.
Royal NP Seven records of singles, Waterfall area 1925 (E. Nubling per E.S.
Hoskin); singles 29.11.57, 15.5.63 (E. Wood, J. Rhodes per E.S.
Hoskin).
West Pennant Hills Pair 6.11.55 (K.A. Hindwood per E.S. Hoskin).
Gordon Pair May -Aug. 1959 (K.A. Hindwood per E.S. Hoskin).
Cattai Pair Mitchell Park 29.6.61 (N. Fearnley per E.S. Hoskin).
Bayview Two birds June 1962 (G. Chapman per E.S. Hoskin). Recorded
Church Point April -May 1979 (G. Stevens/Atlas).
East Lindfield Pair with fledgling Oct. -Nov. 1962 (J. Purnell, K.A. Hindwood per
E.S. Hoskin).
Normanhurst One bird 15.11.69 (J. Purnell per E.S. Hoskin).
Hornsby Recorded between 1966/67 and 1976; Sept. 1978 (E.G. Reynolds
R.M.Cooper/Atlas); winter 1979 (H. Dowd/Atlas).
S36 Debus & Chafer Powerful Owl October 1994
:Killara? Recorded in 10′ block, presumably in bushland of upper reaches of
Middle Harbour, between Mar. and Nov. 1978 (E. Lisser/Atlas).
Marra Marra NP Recorded 5.4.80 (D. Larkins/Atlas).
Newport Recorded Oct./Nov. 1980 (F. Creer/Atlas).
Morton NP Specimen (AM 0.55271), Yarrunga Creek 17.5.81.
Appin Breeding pair Sept. 1981 (L. Klumpes).
Tahmoor Road kill on highway N of Mittagong 20.11.82: adult male, 1469 g
(AM 0.56928).
Kuring-gai Chase NP One bird Bobbin Head 1985 (F. Creer per E.S. Hoskin).
Mandalong Ra. Two nestlings found July 1990 when timber -cutters felled nest tree
for firewood; birds now housed at Featherdale Wildlife Park (per
R. Webb).
South Coast:
Clyde River Specimen (ANWC 18201): c. 13 km SSE of junction with Boyne
Ck, Nov. 1975; male, 1700 g.
Jervis Bay Recorded May- June 1977 (C. Davey/Atlas). Adult male found,
transferred toTaronga Zoo but dead on arrival 29.4.92; suspected
poisoning (per G. Phipps).
Eden One bird Towamba Dec. 1977, and recorded at Eden 1.3.78 (D.
Barton/Atlas).
Bermagui NR Recorded Sept. 1978 (C. Davey/Atlas).
Brogo River Recorded autumn 1978; summer 1978-79 and 1979-80 (T. Moore/
Atlas).
Tathra-Bega Recorded Jan./Feb. 1981 (P. Smith/Atlas).
Nowra Female specimen (road -kill?) from Currambene Creek, fledgling
(ANWC 40919) 30.11.87, “casuarina forest”; 1235 g. Slightly
injured fledgling found near Nowra by bushwalker
bird now housed at Featherdale Wildlife Park (per R. Webb).
Northern Tablelands:
Tenterfield Clutch (C/2) Mt MacKenzie 7.6.53 (T. Allen egg collection). Two
clutches (C/1, C/2) Boonoo Boonoo Ra. June 1958 (AM 0.40391,
40392). Clutch (C/2), “Tenterfield” 23.5.65 (T. Allen collection).
C/2 x 2: Cattle Trap Falls 14.6.70, Branch Swamp 26.6.75 (Morton
Oakley Collection, SAM). “Tenterfield”, C/1,19.6.78 (H. Leonard
egg collection). All data per P. Olsen. Interpreted as at least five
sites robbed by egg collector(s), in addition to Leefield and Boonoo
Boonoo (q.v.). Recorded McLeods Ck, Girard SF 10.6.78 (G.
Holmes/Atlas) in company with one of the collectors concerned:
one of the above nest sites.
Tomalla Tops Pair observed late 1950s; sample infertile clutches (C/2) collected
20.6.58, June 1959 (AM 0.61751; see Hyem 1979).
Yarrowitch Bred between 1951 and 1976, and in 1977 (C.H. Young/Atlas);
locally injured bird cared for by this observer 1980s (per NPWS);
recorded Warnes River 29.12.80 (R.M. Cooper/Atlas).
Boonoo Boonoo Clutches (C/2) taken at two sites: 25.5.60, 4.6.75 (private
egg collection; data per P. Olsen).
Leefield Clutch (C/2) 11.5.69 (N. Kolichis egg collection, per P. Olsen).
Carrai SF One bird Daisy Plains Camp 26.12.79 roosting in open forest near
rainforest (B.& H. Haigh/Atlas).
Australian Birds Vol. 28 Supplement S37Armidale Immature roosted for a day on university building, 1980 (D. Jones).
Washpool NP Recorded 1981 (W. Osborne). Pair with 2 fledglings 26.11.87, pair
18.4.88 (J.Courtney).
Werrikimbe NP One bird Mooraback autumn 1986, Cobcroft’s circa 1987
(SJSD).
Liverpool Range One bird Cedar Brush NR 21.5.87 (I. McAllan & R. Morrow).
Ben Halls Gap SF Two birds flushed from rainforest gully in Messmate Eucalyptus
obliqua forest 13.10.89 (H. Hines).
Spirabo SF One bird in recently logged forest 26.10.89 (H. Hines).
Boorook SF One bird near Boonoo Boonoo Falls 26.10.89 (H. Hines).
Gibraltar Range Pairs known in Butterleaf, Gibraltar Range and Mt Mitchell SFs
late 1980s (per J. Courtney).
Chaelundi SF Recorded late 1980s (per H. Hines); immature owl grappling with
Greater Glider on roadside 1990 (D. Read).
Central Tablelands:
Mittagong Specimen (AM 0.1145), registered 1887.
Lithgow Specimen (AM 0.3092), registered 1889.
Mt Wilson Recorded between 1966 and 1976, and in 1977 (E.G. Reynolds/
Atlas).
Kowmung River One bird 14.4.79 (D. Larkins/Atlas).
Wollondilly River Recorded N of Bullio 24.2.78 (L.E. Smith/Atlas).
Penrose SF One bird July 1981 (J.D. Gibson).
Canyonleigh Recorded 1989 (C. Brandis).
Southern Tablelands:
Snowy Mountains Specimen (AM 0.313), registered 1886.
Brindabella Ra. Adult with two fledglings 15.1.61 (NRS).
Braidwood Specimen (ANWC 19786) c. 27 km N, 17.11.76, in Eucalyptus
seiberi and Allocasuarina littoralis woodland; male (?), 1600 g.
Clyde Mountain Recorded most seasons 1977-79 (V. & R. Routley/Atlas).
Blowering Dam One bird May 1981 (J. Armstrong/Atlas).
Crookwell Specimen (ANWC 42304), Kialla, 10 km S, Jan. or June 1989;
male, 1100 g.
Central -west Slopes:
Mudgee One bird April 1978, on Candlebark Eucalyptus rubida ridge at the
head of a narrow cleared gully, amid hilly dry sclerophyll forest (P.
Lipscombe/Atlas). “Young fledgling” [=nestling?J found by earth –
mover July 1989, presumably when nest tree felled; bird now housed
at Featherdale Wildlife Park (per R. Webb).
South-west Slopes
Wagga Wagga Undated record Livingstone SF (A.R. McGill).
S38 Debus & Chafer Powerful Owl October 1994
:Masked Owl with Black Rat Rattus rattus
Sketch Steve Tredinnick
Australian Birds Vol. 28 Supplement S39THE MASKED OWL Tyto novaehollandiae IN NEW SOUTH WALES
S.J.S.DEBUS’ and A.B. ROSE2
‘Zoology Department, University of New England, Armidale 2351
2Associate, The Australian Museum, 6-8 College Street, Sydney 2000 (present address: 61
Boundary Street, Forster 2428)
SUMMARY
Records of the Masked Owl Tyto novaehollandiae in New South Wales (n=197; 133 post –
1970) were analysed for regional patterns of distribution. Data on diet and breeding biology were
also collated. The Masked Owl occurs mainly in coastal and subcoastal forests and woodlands, but
extends to the far west in River Red Gum Eucalyptus camaldulensis. The Owl’s density appears to
be highest in regions with the greatest local diversity of forest and woodland structural formations.
Its diet in disturbed areas of coastal NSW consists mainly of terrestrial mammals (many of which
are introduced species) caught in forest and woodland, and adjacent open country. The few nest
hollows found have been in tall live or dead eucalypts, in habitats ranging from farmland to rainforest
(primarily eucalypt forest); eggs are laid from autumn to spring. The Masked Owl may be secure
in coastal forested regions, though not necessarily so in intensively logged forests, but threatened
in cleared and overgrazed inland areas.
INTRODUCTION
The range and status of the Masked Owl Tyto novaehollandiae in New South Wales have
been given as “Uncommon, all regions, apparently more numerous in east than west, all terrestrial
habitats”(Morris, McGill & Holmes 1981). This was defined as a total population of 1000-10 000
birds in the State, with records from all the climatic regions delineated by Figure of Morris et al.
1
(1981). The Masked Owl was recorded in only 12 one -degree blocks, all coastal, in NSW during
the Atlas of Australian Birds project (Blakers et al. 1984). Although recent work has shed some
light on the Owl’s biology (Debus 1990, 1993a,b; Kavanagh 1992; Kavanagh & Peake 1993;
Davey 1993), it remains poorly known, particularly in non -forest habitats. Morris (1990) suggested
that it may be “the least common and most threatened of all the Australian owls”, and cited clearance
of forests for agriculture on the NSW tablelands and slopes as a threat. The Owl is classified under
the NSW National Parks and Wildlife Act on Schedule 12, Part 2, “vulnerable and rare” (i.e. small
population in the State). Surveys have revealed that the Masked Owl is recorded less frequently
than other large forest owls in eastern New South Wales (O’Brien 1990; Davey 1993; Kavanagh &
Peake 1993; Kavanagh & Bamkin in press; Debus unpubl. data; R. Kavanagh unpubl. data). There
are fewer NSW records for the Masked Owl than for the other forest owls (this study; other papers,
this issue).
Like other large forest owls the Masked Owl may be a “management indicator” species,
because as a predator of vertebrates it is at the top of the food chain and hence may reflect the
ecological integrity of its environment (see Kavanagh 1991). As a contribution towards the
understanding of the Masked Owl, we here review its occurrence in New South Wales. We also
present data on its diet, and review its breeding biology in the State. This may enable inferences to
be made about its ecological requirements and conservation needs in New South Wales. We also
update previous information on field identification, detection and voice of the Masked Owl (Debus
1990). A detailed review of some aspects of the Masked Owl’s biology is provided elsewhere
(Debus I 993a).
S40 October 1994HISTORICAL BACKGROUND
In mainland Australia generally, and in New South Wales specifically, the Masked Owl
has traditionally been regarded as rare or uncommon, or at least rarely encountered, and poorly
known (McGill 1960; Fleay 1968, 1981; Calaby 1976; Pizzey 1980; Schodde & Mason 1980;
Blakers et al. 1984; Slater et aL 1986; McAllan & Bruce 1989; Hollands 1991). In coastal forests
of NSW it is encountered less often than the Sooty Owl Tyto tenebricosa (Hyem 1979; O’Brien
1990). However, its perceived rarity is in part a detection problem related to its habits, the similarity
of pale males to the Barn Owl Tyto alba, and to observer unfamiliarity (Fleay 1968; Beruldsen
1980; Blakers et al. 1984; Hollands 1991; Garnett 1992). Recent surveys, using appropriate methods,
have detected the Masked Owl at many sites in coastal NSW but nevertheless with lower frequency
than the Sooty Owl or Powerful Owl Ninox strenua (Davey 1993; Kavanagh & Peake 1993;
Kavanagh & Bamkin in press). Hollands (1991) found “good populations” of the Masked Owl in
north Queensland. The Masked Owl is believed to have declined in abundance in historic times;
this has been attributed to a decline in its food resources, to habitat clearance and to destruction of
potential nest trees (Schodde & Mason 1980; Fleay 1981; Blakers et al. 1984; McAllan & Bruce
1989). Habitat clearance on the NSW coast is seen as a continuing threat (O’Brien 1990).
Opinion on the Masked Owl’s mainland distribution and habitat has varied. It was regarded
as inhabiting coastal forest, west to the higher slopes of the Divide, in New South Wales (McGill
1960). Later authors gave its range and habitat as eucalypt forest (but usually not rainforest),
woodland, adjacent cleared country and timbered watercourses over most of Australia except the
most arid central regions; and caves and rock shelters in treeless areas (Fleay 1968, 1981; Slater
1970; Macdonald 1973; Calaby 1976; Pizzey 1980; Beruldsen 1980). This was tempered by more
recent opinion that the Owl’s range has contracted from some inland areas, and that it is now
restricted to forest and dense woodland in a coastal strip <300 km wide (Schodde & Mason 1980; Blakers et al. 1984; Schodde & Tidemann 1986). However, this view requires reassessment in the light of confirmed inland records (Francis 1992; Debus 1993a; this paper), and the continued existence of the Nullarbor Plain population (Blakers et al. 1984). There is no firm evidence of a contraction in its gross continental range in historic times (Garnett 1992). The Masked Owl is said to require a greater diversity of habitat than the Sooty and Powerful Owls: eucalypt forest for roosting and nesting, and forest edge and open woodland for hunting, and therefore requiring a large home -range of 500-1000 ha per pair in coastal forested areas, with neighbouring pairs well separated (Schodde & Mason 1980). This is tempered by the finding that in north Queensland, pairs breed in remnant creekside woodland and forage mostly in adjacent agricultural land where suitably sized prey is abundant (Hollands 1991). The Masked Owl roosts in tree hollows, caves, crevices in cliffs, and in thick foliage in dense gullies (Slater 1970; Calaby 1976; Pizzey 1980; Beruldsen 1980; Schodde & Mason 1980; Blakers et al. 1984). Foliage roosting is said to be infrequent (Schodde & Mason 1980; Schodde & Tidemann 1986), but this view needs reassessment in the light of observations in dense forest (see below; also Peake et al. 1993 and Debus 1993a). The Masked Owl also nests in hollows in trees or cliffs, or in caves (e.g. Calaby 1976; Hyem 1979; Pizzey 1980; Schodde & Mason 1980). Tree nest -sites have been characterised as vertical hollows in trunks or spouts 10-30 m above ground, and c. 0.5-5 m deep x 0.5 m wide, situated in or near eucalypt forest or thick woodland (Beruldsen 1980; Schodde & Mason 1980). However, Hollands (1991) observed nests in more open habitats and isolated trees. Egg -laying extends over many months in the wild (Hyem 1979; Schodde & Mason 1980; Hollands 1991); captive Masked Owls can raise two or three broods in a year (Fleay 1968, 1981; Spencer in Debus 1993a), which suggests that this may occur in the wild if food is abundant. Australian Birds Vol. 28 Supplement S41The Masked Owl’s diet consists of a range of arboreal and terrestrial mammals, mainly small terrestrial species <600 g (Schodde & Mason 1980; Kavanagh 1992; Mooney 1992, 1993; Debus 1993a). The Owl now includes introduced rodents and rabbits in its diet, which in at least some areas compensates partly for the decimation of the native small -mammal fauna in agricultural and pastoral areas of southern Australia (Schodde & Mason 1980). From the foregoing, it is apparent that the Masked Owl may be more numerous and widespread on the Australian mainland (and within NSW) than is generally believed. Furthermore, it has some flexibility in foraging, roosting and breeding habitat, and in diet, and has some of the inherent Tyto breeding flexibility and high reproductive potential. The impact of forestry The role of forest owls as “management indicators” and “keystone” species, in relation to timber production, has been discussed by Milledge et al. (1991) and Kavanagh (1991), and the potential vulnerability of these owls to forest management practices has been discussed by Garnett (1992). The Masked Owl persists in native forests managed for timber, where suitable hollows are available; it occurs in plantations (native species and exotic pines); it often hunts along roads; and it eats terrestrial mammals, including introduced species (Schodde & Mason 1980; Garnett 1992; Kavanagh 1992; Davey 1993; Kavanagh & Peake 1993). For the Masked Owl, the main concerns in relation to timber harvesting are the continued availability of standing hollow trees for the Owl’s roost and nest sites, and the maintenance of suitable foraging habitat (a mosaic of dense and sparse ground cover: Peake et al. 1993). Some management practices may reduce habitat quality by removing resources used by the Owl’s prey, e.g. logs or ground cover. Intensive logging causes a decline in native ground -dwelling small mammals (Dickman 1991 and references therein). Cool, autumn prescribed burns at high frequency disadvantage many small native mammals (ground – dwellers and some arboreals), but advantage exotic mice, rats and rabbits (Catling 1991), therefore the effect of fire on the Owl’s food supply may be equivocal. Nevertheless, the Masked Owl was recorded at a greater proportion of sites in unlogged than in logged forest in the Eden region (7% vs 3%), although the small sample size rendered the difference non -significant (Kavanagh & Bamkin in press). The difference may be related to the effect of logging and associated impacts on the abundance and diversity of terrestrial native mammals, or their accessibility to the Owl in dense post -logging regeneration. It is by no means certain that in wood -production forests, the Masked Owl is of less concern than the Sooty and Powerful Owls. Furthermore, the Masked Owl may be threatened in forests and woodlands subject to clearfelling for agriculture or coastal development. About 20% of the tall open forest, 50% of the open forest and perhaps 70% of the woodland in NSW has been cleared (from Lunney 1991). This suggests that the Masked Owl’s population may have declined by almost 50% in formerly forested areas, and more than 50% in former woodland areas, in NSW. METHODS Records of the Masked Owl in NSW to December 1992 were collated from the literature, museums (Australian Museum [AM], Queensland Museum [QM], Museum of Victoria [MV], Australian National Wildlife Collection [ANWC]), the RAOU Atlas of Australian Birds (unusual record forms), the Keith Hindwood Bird Recording Service (per E.S. Hoskin), colleagues’ unpublished notes, and our personal records (Appendix 1; excludes those of SJSD’s and R. Kavanagh’s current owl surveys, which will be published later). Literature records were obtained from the following sources (details in Appendix 2): Emu; Corella; Australian Bird Watcher; Australian Birds; Canberra Bird Notes; the NSW Field Ornithologists Club annual bird reports S42 Debus & Rose Masked Owl October 1994 :1970-1991 inclusive; NSW FOC Newsletter unusual records series by Morris & Chafer 1988- 1992; Australasian Raptor Association News; books, reports and other publications (Sturt 1849; North 1911; Hindwood & McGill 1958; Fleay 1968, 1981; Gibson 1989; Hollands 1991; Hoskin et al. 1991; Kavanagh 1992; Shields et al. 1992; Kavanagh & Peake 1993; Davey 1993). Some records were reported by more than one source, therefore care was taken not to double -count records. One record was taken as one bird at one locality in one year (i.e. two birds = two records), and nestlings were not counted. Records were analysed as the number of sites at which the Masked Owl has been reported, a site being defined as the area within which a cluster of records can be reasonably assumed to represent a single occupied Owl territory. Owl sites were located on topographic maps and assigned to the botanic provinces of Anderson (1961); in borderline cases allocations were made on the basis of altitude and known or inferred vegetation type at that site. Habitat classifications were derived from observers’ sightings, where habitat details were reported by literature or informants, and from site descriptions for our personal sightings of Masked Owls. Prey data were collated from the literature, and from Masked Owl pellets, prey remains and sight records of Masked Owls with prey, obtained by ABR and colleagues since 1970. Prey species, and the minimum number of individuals, in the examined dietary samples were identified and quantified from skull count or other skeletal elements, by ABR from reference material in his personal collection and in The Australian Museum, with the assistance of literature (Thomas 1888; Knox 1976; Watts & Aslin 1981). We made the following assumptions about the prey data: (1) A sample of five pellets from Alstonville in 1988 was deposited by a Masked Owl, because it was reported as such by NPWS ranger R. Moffatt, an ornithologist; his informant (B. Baigent, an experienced bird -watcher) had seen the roosting owl. The pellet sizes (22 x 18 to 64 x 33 mm) and prey species could fit either Masked or Barn Owl (cf. Schodde & Mason 1980), but are here accepted as Masked. (2) Following Mooney (1992, 1993) and Peake et al. (1993), we assumed that all Long -nosed Bandicoots in the diet samples were juveniles, and that juvenile mammals were half adult weight. RESULTS Distribution An analysis of 197 records (133 since 1970) shows that the Masked Owl is thinly distributed over much of New South Wales (Figure 1). The Owl has been recorded in 15 (88%) of the 17 New South Wales regions defined by Morris et al. (1981), with greatest frequency in coastal regions, and a scattering of records inland to the far west, where it has been recorded only in River Red Gum Eucalyptus camaldulensis. The coast (127 sites, 81%) appears to be the most important region, followed by the tablelands (15 sites, 10%), plains (10 sites, 6%), far west (5 sites, 3%) and slopes (nil; total 157 sites). The coast is the zone with the greatest number of observers but, as discussed below, this pattern is not simply an artifact of observer distribution and density. Australian Birds Vol. 28 Supplement S43153° 150° 151° 152° 149° 141° 142° 143° 144′ 45° 146′ 147° 14.50 III U I 34° 35′ 36′ 37. Figure 1. Distribution of Masked Owl in New South Wales, in ten-minute grids. Two records not included because exact localities unknown: Charles Sturt’s specimens from the Murray River below the Mu rru mbidgee (Stenhouse 1930) and Darling River below Menindee (Sturt 1849). S44 Debus & Rose Masked Owl October 1994 :Table 1 Number of sites at which the Masked Owl has been recorded, in each of the regions defined by McAllan & Bruce (1989). For repeat Owl records, or pairs/families, a “site” is defined as the area in which a cluster of records represents an occupied Owl territory. Botanical attributes of regions summarised by Anderson (1961). For wooded habitats within each region, RF = rainforest, F = eucalypt forest, W = woodland. Wet F = wet sclerophyll (tall open) forest; dry F = dry sclerophyll (open) forest. Charles Sturt’s specimen for the Murray River below the Murrumbidgee (Stenhouse 1930) not included. Region n Habitats in region North Coast 41 26 RF, wet F, dry F, W, heath Central Coast 50 32 RF, wet F, dry F, W, heath South Coast 20 13 RF, wet F, dry F, W, heath Northern Tablelands 19 12 RF, wet F, dry F, W, heath Central Tablelands 3 2 RF, wet F, dry F, W, heath Southern Tablelands 8 5 Wet F, dry F, W, heath North-west Slopes 0 0 Dry F, W Central -west Slopes 1 Dry F, W South-west Slopes 0 0 Dry F, W North-west Plains 7 4 Riparian W, Dry W South-west Plains 5 3 Riparian dry F, dry W, mallee North Far Western Plains 2 1 Riparian W South Far Western Plains 1 1 Riparian W, mallee Total 157 The New South Wales regions defined by McAllan & Bruce (1989) are based on botanical provinces, and hence better reflect habitat types, if only broadly. The Masked Owl has been recorded in 11 (85%) of these 13 regions, again with greatest frequency on the coast (1 1 1 sites, 71%) and tablelands (30 sites, 19%), with fewer records on the slopes (1 site, 1%), plains (12 sites, 8%) and far west (3 sites, 1%; total 157 sites: Table 1, Figure 2). The high total for the coast coincides with the greatest local or regional habitat diversity, in terms of vegetation structural formations: a local mosaic of closed forest (rainforest), tall open (wet sclerophyll) forest, open (dry sclerophyll) forest, woodland and open areas ( Table 1). 60 120 50 100 40 so 30 60 20 40 10 11111.1M____Mliw, 20 0 NC CC SC NT CT ST PINS CWS SWS NWP SWP NFWFSFWP 0 Coast Tablelands Slopes Plains Fa, We.: Regions Zones Figure 2. Number of sites with Masked Owl records according to botanic region and botanic/ moisture zone (after Anderson 1961 and McAllan & Bruce 1989) Australian Birds Vol. 28 Supplement S45It is worth considering the western records further, to establish their validity, particularly as many were ignored or discounted by Schodde & Mason (1980). Lower Darling River: Sturt (1849) collected a specimen downstream from Menindee (32°21’S, 142°26’E), after startling it out of a riparian tree [presumably the foliage canopy rather than a hollow, and presumably in daylight]. He described it as “very rare in the interior”, whereas the Barn Owl was common and “inhabits the interior in great numbers”. Sturt previously collected a Masked Owl on the Murray River downstream from the Murrumbidgee in the “interior of New South Wales” (Stenhouse 1930), but it is not certain whether it was collected in what is now South Australia because he reached the Murray mouth. The latter specimen is in the National Museums of Scotland, Edinburgh (NMS 1830.2, labelled “Banks of River Murray [1830]”; B. McGowan in Litt.). The whereabouts of the Darling River specimen could not be ascertained; it is not in the British Museum (Natural History), Merseyside Museum (Liverpool, UK), National Museums of Scotland, American Museum of Natural History or Academy of Natural Sciences, Philadelphia (M. Adams, A. Parker, B. McGowan, M. LeCroy in lift.). Riverina: K.H. Bennett (in North 1911) stated that Masked Owls were numerous in the Mossgiel district (“Yandembah”, 33°27’S, 144°55’E) in the early days of settlement, during a rat plague (presumably Long-haired Rat Rattus villosissimus), and preyed on the rats. His unpublished list of fauna (Bennett n.d.) shows that he observed two species, Masked Owl and Barn Owl. Furthermore, that year (1864) was an exceptional season in which Letter -winged Kites Elanus scriptus and Flock Bronzewings Phaps histrionica appeared; he saw what were evidently stick- nest rats Leporillus sp.; and Burrowing Bettong Bettongia lesueur, a bandicoot sp. and Brown Hare -Wallaby Lagorchestes leporides were present. This rich small -mammal fauna existed when stock had been in the area for only two years, and before the rabbit invasion. The situation appears to parallel that in the Mt Lofty Ranges/Murray Mallee of South Australia, where Gould (1843) found the Masked Owl common. In Bennett’s area, after the build-up of stock and the rabbit invasion, the small – mammal fauna collapsed and the Masked Owl disappeared. Nyngan: Specimen in the H.L. White collection, Museum of Victoria (HLW 5314), 14 October 1890, ex Robert Grant collection. This record has been doubted by Schodde & Mason (1980) and others on the grounds that many of Grant’s localities were unreliable, but in this case the locality and other details would seem specific enough: “Captured in trap set for Bilby [Macrotis lagotis] on Graweed Station, near Nyngan (NSW)”. Grahweed (31°21’S, 147°00’E) is 30 km north-west of Nyngan (which is on the Bogan River). Although clearing has taken place, there is still some mature eucalypt woodland apparently suitable for Masked Owls, and River Red Gum along the river (SJSD pers. obs.). Note also recent Nyngan record (discussed below). Whitton (34°31’S, 146°11’E): female specimen, AM 0.17008, registered in 1912. Narrabri (30°25’E, 149°55’E) 24.10.1937: characteristic call heard at night, on Namoi River [presumably in River Red Gum] 13 km south-east of town, by ornithologist A.J. Elliott who noted (unpubl. notes): “I heard the hissing keek of this species – at least I would be very surprised to learn that the bird responsible was not of this species”. Elliott (1935) was familiar with the Masked Owl, having previously observed its breeding cycle on his property and hand -reared a fledgling. With experience, its call is distinguishable from that of the Barn Owl. Note also recent Narrabri record, discussed below. Deniliquin (35°32’S, 144°57’E), January 1955: a pair nested and raised two young (Hobbs 1961). The observer, now deceased, was an experienced ornithologist with an impeccable record in such matters. His account deals with all the other owls occurring in the region, and includes mention of many encounters with Barn Owls, with which he was familiar. S46 Debus & Rose Masked Owl October 1994 :Broken Hill, 1968 (Beruldsen 1969, 1972): bird on Marrapinna Station (30°56’S, 142°03’E) identified by call, on the basis of prior and subsequent experience of Masked and other owls. The observer is an experienced ornithologist. Bird was on Nuntherungie Creek in River Red Gum, and was identified as Masked Owl on the following grounds: author’s familiarity with Barking Owl Ninox connivens, Barn Owl and Masked Owl screaming/screeching calls elsewhere; calls too loud and low-pitched for Barn; identical calls subsequently heard in forest in south-east Queensland, and imitated, whereupon a large Masked Owl approached (G. Beruldsen in lift.). Broken Hill, 31.8.74 (Rogers 1975): pair “at a nest”, Fowlers Gap (31°08’S, 141°40’E) 110 km north of the city, seen by the late A.R. McGill. The observer, an experienced ornithologist and one of the “fathers” of modern ornithology in NSW, had an impeccable record in such matters. McGill’s diary notes read: “Masked Owl: when I ‘tapped’ a large gum in the creek [in daylight] a male flew out to be followed by the much larger & darker female, which was followed for 200 yards distance” (A.R. McGill unpubl. journal of personal ornithological observations, Aust. Museum archives). Given McGill’s familiarity with common owls, he obviously knew the difference between Ninox and Tyto species. From the birds’ sexual size and colour dimorphism, his identification of these two owls was clearly correct. However, the “nest” was an unwarranted assumption as the pair could simply have been roosting together. Nyngan (31°34’S, 147°12’E), 25.11.76 (Rogers 1977): two birds seen by A. Rogers, T. Kenney and B. Finch, all experienced observers; the record would not have been accepted for the FOC annual bird report for that year if there had been any doubt. The birds were observed at about 02:00 hrs, c. 2 km south-east of the town, in open country. They were perching on roadside fenceposts, and allowed close observation by spotlight and binoculars; they were larger and darker than Barn Owls. They were seen well, and for as long as the observers wanted, i.e. they did not flush (A. Rogers pers. comm.). Conclusive diagnostic features were the darker facial discs (compared with Barn Owl), and the feathered legs and feet which were clearly visible (copy of T. Kenney’s notes, per A. Rogers). Jerilderie (35°22’S, 145°43’E), 26.4.82 (Lindsey 1984): two birds in River Red Gum at night, identified by diagnostic call low overhead (G. Holmes in litt.). The observer is an experienced ornithologist, with other observations of this species in eastern NSW (Appendices 1 and 2), some by imitation or by playback of taped calls. Gunbar (34°04’S, 145°25’E), 6.9.84 (Lindsey 1986): owl flushed from hollow in large roadside dead tree, in fine weather in daylight, and perched in nearby stand of trees. Similar in colour to Barn Owl (back and wings brown and grey, underparts pale), but larger (c. 50 cm), particularly in flight; very noticeable and well -marked black edge to facial mask; feet large; legs thick and feathered, “fluffy”; observers familiar with Barn Owl; owl identified as pale morph female Masked Owl and discussed with A.R. McGill (J. & N. Russill in litt.). Narran Lake Station, south-east corner of Narran Lake (29°55’S, 147°25’E), 6.5.85: owl perched at night about a metre from the top of a burnt -out Callitris pine 4.5 m tall, in woodland. Viewed in spotlight and binoculars from a distance of 10 m from base of tree for almost a minute, by J. Pegler, R. Bolton, J. Duranti, R. Murray, N. Maxwell and other FOC members, who had a clear and uninterrupted view. It was pale grey with light grey wings, and was concluded to be a pale morph Masked Owl rather than a Barn Owl because of its large size and the thickness of its legs. The lake was full at the time. Narrabri (30°25’S, 149°50’E), August -November 1989: one bird seen regularly at close range, on roadside fenceposts at night, c. 12 km south-east of town. Compared with Barn Owl it stood taller and was darker in plumage; it was more difficult to flush and less wary than Barn Owls. It was Australian Birds Vol. 28 Supplement S47always on the same 200 m of roadside fence (D. Richards in litt.; observer is an experienced ornithologist, familiar with Barn Owl). All these inland records are eclipsed by a verified record of a Masked Owl at the Coongie Lakes, north-eastern South Australia (Francis 1992). HABITAT Forty-nine nocturnal records of Masked Owls (including road kills) could be referred to a specific structural habitat. Of these, five (10%) came from tall open forest (= wet sclerophyll); 13 (27%) from open forest (= dry sclerophyll); eight (16%) from either open or tall open forest; seven (14%) from forest/farmland interface; seven (14%) from wooded farmland; three (6%) from riparian woodland (River Red Gum); two (4%) from treed urban areas; two from woodland (4%); and one each from Hoop Pine Araucaria cunninghamii plantation (2%) and sugar cane (2%). That is, half of the sightings were from open or tall open forest, two-thirds were from forest or woodland, and many of the remainder were from forest or woodland edge or adjacent open country. At least seven of these sightings (14%) were made along roads or tracks, and 39 records (20% of the entire 197 NSW records) were of road kills or road injuries, indicating that Masked Owls make use of the edge effect created by roads through wooded habitats (although roads are the most intensively sampled habitat). Most (c. 80%) of the road kills were from the Pacific or Princes Highway or adjoining secondary roads, through forested or partly forested areas of the coast. Five records were of Owls killed or injured on barbed-wire fences or under powerlines, indicating that the Masked Owl makes use of artificial (roadside) perches in modified landscapes; the Owls probably strike unseen wires while flying between perches. Some Masked Owls living in forest forage in adjacent open country (e.g. Hyem 1979; Debus 1990), but some Owls live, forage and breed entirely within forest, kilometres from the nearest open country (Roberts 1983; Kavanagh 1992). However, even these records were obtained from road/track edges where the Owls can take prey from areas of open ground. There is insufficient information for conclusions on the floristics (eucalypt associations) of the foraging habitats preferred by Masked Owls. From the distribution of the Masked Owl across the botanical regions (Table 1 of this paper), and the occurrence of eucalypt alliances in these regions (Table 2.1 of Specht et al. 1974), the Masked Owl potentially occurs in most of the major eucalypt forest and woodland alliances of the coast and tablelands. This supposition is supported by the variety of eucalypt alliances in which it has been recorded (Table 3 and Appendix 1, this paper; Table 4 of Kavanagh & Peake 1993). However, it may have preferences for particular forest types with a dry and open understorey and which provide a mosaic of dense and sparse ground cover (cf. Peake et al. 1993). Farther west, the Owl occurs in River Red Gum forest and woodland and probably (or formerly) in box-ironbark forests of the slopes and box woodlands of the plains (as noted by Bennett in North 1911). ROOSTING SITES As well as the more usual tree hollows (Hyem 1979; Marchant 1979; Kavanagh 1992), Masked Owls sometimes roost in daylight in thick vegetation in the “heavily timbered… and open forest lands near the coast” (North 1911), or in caves, in New South Wales. Records of “outside” roosting in trees include 8 m above ground in an exotic pine in suburban Sydney and under the canopy of a Cabbage Palm Livistona australis in palm forest at Avalon (K. Hindwood per E. Hoskin); vine -covered Stinging Tree Dendrocnide excelsa and other trees in rainforest gullies in the upper Manning Valley (Hyem 1936, 1979); a lemon tree on a rural property at Araluen (Gregory – Smith 1986); a tree on a well -timbered road verge near Mittagong (F. Harrap in lilt.); a large Tallow -wood Eucalyptus microcorys in wet sclerophyll forest near Lismore (B. Baigent; see Appendix 1); and creekside vegetation in forest at Helensburgh (D. Rayment per C.J. Chafer). S48 Debus & Rose : Masked Owl October 1994These cases are all from the heavily vegetated coast and tablelands. Farther inland, where foliage cover is sparser, the Owl’s roosting opportunities are restricted to tree hollows (Bennett in North 1911; examples in this paper) or caves. Records of cave roosting in NSW include a Masked Owl flushed from a rock overhang in Ku-ring-gai Chase by NPWS ranger I. Cranwell (pers. comm.), and a Masked Owl skull found in a rock overhang at Seal Rocks (ABR). The skull was identified as this species, because it matched perfectly a skull taken from a road -killed Masked Owl (ABR). DIET The diet samples came mainly from disturbed areas (roadsides, farmland). The Masked Owl’s diet in such areas in eastern New South Wales consists mainly of small and medium-sized terrestrial mammals (Table 2): of 27 mammals in our sample, 22% were marsupials, 70% rodents and 7% rabbits by number; 81% of these <400 g. Most of these were terrestrial (67% by number; n = 24), with some arboreal (13%) and some both (active on ground and on trunks and branches, i.e. scansorial, 21%; prey habits from Strahan 1983). That is, at least two-thirds of captures were made on the ground. By biomass, which better reflects dietary importance, prey was 61% terrestrial, 8% arboreal and 31% scansorial. Only the Sugar Glider Petaurus breviceps requires tree hollows, and it is not restricted to old -growth forest (Strahan 1983). This suggests that at least in its foraging ecology, the Masked Owl is not reliant on mature forest although a small proportion of its prey requires den sites in standing hollow trees. However, most of its native terrestrial prey may need the resources provided by mature trees (cf. Catling 1991, Dickman 1991). Table 2 Diet of the Masked Owl in coastal New South Wales (mainly disturbed areas): minimum number of prey individuals where diet quantified, otherwise presence only (X). Main habits of mammals: T = terrestrial, S = scansorial, A = arboreal. Mean or median adult prey weights from Strahan (1983). Juveniles assumed to be half adult weight. For diet samples, M = miscellaneous specimens (gut contents), sightings and pellets from coastal NSW, ABR and colleagues (including Australian Museum data); L = literature (Elliott 1935; Fleay 1968; Hyem 1979; Roberts 1983; Schulz 1987). Species Weight Main M L Total (g) habit Long -nosed Bandicoot (juv.) Perameles nasuta 488 T 3 3 Sugar Glider Petaurus breviceps 128 A 2 1 3 Hastings River Mouse Pseudomys oral is 95 T 1 1 Bush Rat Rattus fuscipes 125 T 1 1 2 Black Rat Rattus rattus 280 S 4 X 5+ Rattus sp. 176a T/S 2 X 3+ House Mouse Mus musculus 18 T 6 6 Mouse sp. (Mus?) 18 T 2 2 Rabbit Oryctolagus cuniculus: age not stated 500b T 1 X 2+ Unidentified mammal 3 3 Total 25 5+ 30+ a mean of Rattus spp. b assumed to be immature, c. 500 g Australian Birds Vol. 28 Supplement S49Four of the seven identified mammal prey species inhabit forest or woodland only; the remaining three also inhabit open areas (Strahan 1983). Of the specifically identified prey individuals, nine (38% by number) were from forest or woodland and 15 (63%) from forest/woodland or open areas; i.e. more than a third of captures were made in forest or woodland. In terms of dietary importance, 45% of mammal biomass came from forest/woodland and 55% from both forest/ woodland and open country. That is, almost half of mammal prey biomass came from forest/ woodland and the remainder probably came from the interface between forest or woodland and open country. However, even the forest data- collection sites were disturbed by roads, tracks or forestry activities which provide edge effects (see Appendices and 2). 1 Fifteen (63%) of the 24 identified prey mammals were introduced species, 55% by biomass, indicating the importance of exotic mammals in the Masked Owl’s contemporary diet in disturbed areas in coastal NSW. This contrasts with the absence of exotics from the Masked Owl’s diet at a forest site in NSW (Kavanagh 1992), which suggests that the Owl opportunistically takes the locally most abundant or available ground mammals. The diet sample was small, and some caution is therefore needed. The percentage figures for exotic mammals are minima, and it is possible that the Masked Owl’s diet in disturbed areas contains even more exotic rats and rabbits than suggested by Table 2. BREEDING The Masked Owl breeds in a variety of wooded habitats, but most of the few nest hollows found in New South Wales have been in live eucalypts in open or tall open forest, including emergents in rainforest (Table 3; mean nest entrance height = 17 m above ground). The Owl has a wide tolerance of nest habitats and sites, as shown by additional nest records (Hobbs 1961; Rogers 1975) not listed in Table 3. One concerns an undated record of a pair attempting to breed (apparently unsuccessfully) in a dead tree, in the garden of a Sydney suburban house near bushland and farmland: one bird was in the nest hole, and the other habitually flew to the hole at dusk (E. Smith per E.S. Hoskin; further details unavailable). The pair observed by Hobbs (1961) “nested” at Deniliquin in January 1955 (presumably in River Red Gum) and reared two young. The successful nest observed by Elliott (1935) was in a dead tree in a paddock, some hundreds of metres from a forested hillside. One nest hollow was a metre deep (Jackson 1907), and another was three metres deep (Hyem 1979). Data on breeding density and home -range size are almost non-existent, but in northern New South Wales two pairs, each with a fledgling, were about a kilometre apart (de Warren 1928). Three other pairs were separated by several kilometres (Hyem 1979), but it is not certain that they were neighbours. The home range of one pair was >1 km across in one direction (Debus 1990).
This is similar to an inter -nest distance of at least 1.5 km and a minimum density and inferred
home -range size of 2 km2 per pair for Tasmanian Masked Owls (Mooney 1992, 1993). However,
it is a higher density than the 5-10 km2 per pair postulated by Schodde & Mason (1980).
S50 Debus & Rose Masked Owl October 1994
:Table 3
Breeding parameters of the Masked Owl in New South Wales. RF = rainforest, TOF = tall open (wet
sclerophyll) forest, OF = open (dry sclerophyll) forest. E = Eucalyptus. Height = height of nest hollow
entrance above ground. Sources: 1 =Jackson (1907); 2 = North (1911); 3 = de Warren (1928); 4 = Elliott
(1935); 5 = Fleay (1968); 6 = Hyem (1979); 7 = E.L. Hyem/Aust. Museum; 8 = Roberts (1983); 9 = Debus
(1990); 10 = J. Skinner. C/1 = clutch of 1, etc.
Habitat Tree sp. Height Month Stage Clutch/ Source
(m) brood
size (n)
OF(?) E. maculata 6 Nov nestlings B/2 I
OF(?) E. punctata ? June nestling B/1 2
? ? ? Feb fledglings B/1 x 2 3
F/open dead tree 21 July fledglings B/2 4
RF E. grandis 24 Aug hatching C/3 5
TOF E. grandis 25 July eggs C/4 5
RF/TOF edge E. saligna 22 Aug eggs? ? 6
? E. saligna ? autumn eggs? ? 6
? dead tree ? ? nestling B/1 6
? ? ? Mar -Apr laying x 3 ? 6
? ? ? ? eggs C/3 6
? 9 ? ? fledglings B/2 6
OF E. punctata 18 May hatching C/3 7
TOF E.viminalis 5 June fledgling B/1 8
OF E.cypellocarpa la Nov fledgling seen 9
1 1
? large tree May chicks B/2 10
a estimated; given as 18 m (measured) by Kavanagh (1992)
Using data on nestling and incubation periods provided by Schodde & Mason (1980), and
back -dating from the events listed in Table 3, we conclude that laying in New South Wales extends
from late February/early March to late September/early October, commonly March to July. There
is thus some seasonality in laying, most clutches started from early autumn to late winter. Recorded
clutch size in NSW is three or four (C/3 x 3, C/4 x I) and brood size at fledging is one or two (B/1
x 5, B/2 x 3, including the nest observed by Hobbs 1961).
Loss of hollow trees during the breeding cycle is one cause of breeding failure (see Appendix
1). There appears to be a steady attrition of standing hollow trees (potzntial or actual nest sites) in
cleared areas through senility and exposure to winds, and in forests subject to frequent fires. For
example, hollow trees burned through and fell at a rate of at least one per hour for most of a day
during a slow, cool forest fire in mature forest on the Northern Tablelands (SJSD pers. obs.; area of
fire unknown but <5 km2). FIELD IDENTIFICATION, DETECTION AND VOICE At night, Masked Owls can be detected and identified mainly by their calls. Visual confirmation can be made subsquently by spotlight, using the morphological characters discussed elsewhere (Debus 1990, 1993a; Peake et al. 1993). A survey method used with considerable success by SJSD and R. Kavanagh is a period of listening, followed by playback of taped calls then spotlighting, at each site being surveyed (see also Kavanagh & Peake 1993). Australian Birds Vol. 28 Supplement S51Following a further three years of field surveys of large forest owls by SJSD, it is apparent that the shrill scream reported previously (Debus 1990) is very rarely heard (in fact not heard at all during the three years despite >40 Masked Owl contacts, and only once before then). The most
common call is the rich, deep rasping screech, readily distinguished from the Barn Owl’s screech
once the calls of both species are known. This (not the shrill scream, contra Debus 1990) is the call
described by Roberts (1983), and an example of it is the first Masked Owl sequence on the Field
Guide to Australian Bird Song cassette series (cassette no. 5, Bird Observers Club of Australia).
The Masked Owl’s screech is often given singly, sometimes from the roost at dusk or pre -dawn;
there is no truth to a recent bird- watchers’ myth that the Owl only calls at around 03:00 hrs.
Following the use of a better tape-recording for broadcast from mid 1990, Masked Owls
have sometimes responded to playback. The Owls may respond in one of several ways:
(1) A single, sometimes distant, screech in reply, then no further response (common).
(2) Approach silently to a perch, then give a chattering call in reply to each playback
screech (common).
(3) Approach to a perch, and call threateningly with a loud, deep, vibrating screech (rare).
(4) Land silently on a nearby perch, seen only by spotlight (rarely detected, but possibly common).
(5) Circle overhead, above the tree canopy, giving a squeaky chattering call (rare).
The chattering call is the key to detecting a perched owl that has approached silently. This call is a
“hard” cackle or chatter, like a dry stick dragged rapidly across a paling fence: k -k -k -k -k, c. 5
syllables in a second. Sometimes this is given loudly with a squeaky quality, like that given in
circling display flight.
In order to avoid disturbance particularly to breeding birds, playback should be used sparingly
and only to confirm the species’ presence at a site. The recent practice among bird -watchers, of
“twitching” breeding pairs of Masked Owls, may cause unnecessary disturbance to the birds. It
may be more useful, in terms of conservation of the Owl through knowledge of its distribution and
habitat requirements, if Sydney bird -watchers search for Masked Owls in state forests of the Central
Coast and in other bushland areas around Sydney. This is preferable to revisiting already known
pairs, unless the purpose is bona fide long-term monitoring of territory occupancy and breeding
success.
DISCUSSION
The data collated in this paper generally agree with the trend in ornithologists’ perceptions
of the Masked Owl’s biology, ecology and status, and support our initial inferences from the historical
evidence. On the Owl’s distribution in New South Wales, the assessment by Morris et al. (1981) is
more accurate than that by Schodde & Mason (1980), i.e. the Owl does occur far inland. However,
it does not occur in “all terrestrial habitats” but only those with trees of moderate to high density,
and adjacent open areas with perches. The number of records, road kills and successful surveys
suggest that the Owl is not as rare as commonly supposed, at least in coastal NSW, though
nevertheless scarce.
From the data on distribution, habitat and diet we interpret the Masked Owl as primarily a
predator of small terrestrial mammals in eucalypt forest and woodland, and on ecotones between
these and open areas, in coastal and subcoastal New South Wales. Much prey in disturbed areas
consists of exotic mammals, and the Masked Owl captures these in cleared or semi -cleared areas
near remaining forest and woodland. Although the Masked Owl and some of its prey require tree
hollows for nesting and roosting, the Owl roosts in dense foliage or in caves and it nests in disturbed
areas. Habitat clearance and rural tree decline continue, and senile trees left in cleared areas are not
being replaced by natural regeneration, meaning that availability of the Owl’s nest and roost sites is
declining.
S52 Debus & Rose : Masked Owl October 1994The assessment of Morris et al. (1981) on the Masked Owl’s abundance from east to west
seems correct. However, the Owl’s distributional pattern in New South Wales may partly reflect
the distribution and density of observers: most records come from the heavily populated coast.
Nevertheless, the number of records of other nocturnal birds, including uncommon owls, throughout
NSW (in Blakers et al. 1984) suggests that differences in Masked Owl abundance from east to west
are real. The only anomaly in the Masked Owl’s distribution is the cleared Central Division (slopes),
which has almost no Owl records and fewer than adjacent divisions; this may reflect a lack of prey
and/or habitat, or a lack of surveys. We conclude that eastern forested regions support higher
densities of Masked Owls than western sparsely wooded regions; that the Owl is rare and localised
around rich patches such as watercourses in arid and semi -arid areas; and that it has been locally
extirpated in cleared and overgrazed parts of inland NSW. We predict that systematic surveys will
locate it in the larger forest or woodland remnants on the western slopes, e.g. Pilliga Scrub, and
farther inland in riparian situations.
The Masked Owl may seem less abundant than Sooty and Powerful Owls because of
behavioural differences (e.g. lower detectability or response to playback by Masked). However,
the difference in coastal forest may be real and better explained by ecological factors: prime Sooty
Owl habitat (rainforest and wet sclerophyll) may not be prime Masked Owl habitat. In eastern
NSW where they overlap, Masked seems to prefer drier and more open forest with a sparse
understorey and grassy ground cover (Debus, pers. obs.). In NSW the highest densities of Masked
Owls may therefore have been in the drier open forests and woodlands of eastern regions: habitats
extensively cleared, and not surveyed for forest owls.
Data on the Masked Owl’s resource requirements support the explanations given by other
authors for the Owl’s decline in southern Australia. Furthermore, they suggest reasons for a
differential decline in inland versus coastal regions. The Masked Owl’s decline on the coast may
not be severe because, despite some habitat clearance, three or four exotic mammals (Rabbit
Oryctolagus cuniculus, House Mouse Mus musculus, Black Rat Rattus rattus and Brown Rat R.
norvegicus) have been added to a reasonably intact native small -mammal fauna. Also, the Owl
may have been favoured to some extent by the creation of openings in dense coastal and escarpment
forests. Nevertheless, some remaining forest patches may now be less suitable for the Owl’s native
prey, and in some wood -production forests the scenario depicted by Dickman (1991) and Catling
(1991) applies. In some intensively managed forests on the Central and North Coasts, most or all
of the hollow trees have already been removed over wide areas.
By contrast, habitat clearance has been severe in the drier open forests and woodlands of
the tablelands, slopes and parts of the plains (e.g. Lunney 1991). Furthermore, over much of
southern inland NSW a whole suite of native terrestrial small mammals has been replaced by only
two exotic species: an inherently unstable and unreliable supply of Rabbits and House Mice, which
are not optimal prey sizes for the Masked Owl (cf. Mooney 1992, 1993). The addition of the exotic
Brown Rat locally in parts of the Riverina (South-west Plains), and the persistence of a few native
rodents in northern inland NSW, may account for the scattering of recent Masked Owl records in
these regions. The Riverina may have been a rich area for the Masked Owl and its prey before
habitat degradation by stock, rabbits and clearing, and the collapse of the small -mammal fauna.
In eastern NSW the Masked Owl’s preference for open forest, woodland and edge is clear.
In dry forest, the Owl often selects a moist and/or sheltered microhabitat for roosting and nesting,
such as gums in gullies or drainage lines (e.g. Table 3). This apparent selection of locally rich
patches, in terms of moisture and presumably prey densities, concurs with the conclusions of Davey
(1993). Nevertheless, Masked Owls may forage well away from roost/nest sites, and breeding or
Australian Birds Vol. 28 Supplement S53roosting microhabitat may have little relevance to foraging habitat and diet (Tasmania: Mooney
1992, 1993).
The Masked Owl’s prime habitat appears to be a diversity of vegetation structural types
(open/tall open forest, woodland etc.) in a given area, a combination which would provide tall or
dense trees for roosting and nesting, and more open vegetation and ecotones for hunting (cf. Schodde
& Mason 1980). A local mosaic of many habitat types (as on the coast: Table 1) may enhance prey
density and diversity and the Owl’s foraging opportunities, by providing structural complexity.
These conclusions are supported by the findings of Kavanagh & Peake (1993) and Davey (1993)
on the Masked Owl’s occurrence in relation to forest type, logging history, age profile, structure
and local complexity, and associated mammal diversity. Other structural attributes of Masked Owl
habitat, and hollow requirements for the Owl and its arboreal prey in Victoria (Peake et al. 1993),
probably apply to NSW.
Floristics (ultimately determined by soil fertility and moisture) may be important determinants
of prey densities. No particular eucalypt associations have yet been identified as of outstanding
importance to the Masked Owl in eastern NSW, and in the Mt Royal area it was recorded in “all
forested habitats” except rainforest (Shields et al. 1992). Nevetheless, the Owl favours some eucalypt
alliances and avoids others in Victoria (Peake etal. 1993), and its habitat preferences require detailed
investigation.
The Masked Owl’s dietary preferences, and its propensity to switch to exotic prey, are clear
(this study; Kavanagh 1992; Mooney 1992, 1993; Peake et al. 1993 ). It prefers small terrestrial
mammals of <600 g, mean 327 g; mean prey weight of male Masked Owl, the smaller sex, is 97 g (Mooney 1992, 1993). In coastal areas, at least where sufficient remnant forest or woodland remains, the Owl may still have an adequate food supply in the form of native mammals supplemented by exotic rats, mice and rabbits; in disturbed areas, the Black Rat is commonly taken (Hyem 1979). However, in inland NSW with Black Rats and most native mammals in the preferred size range absent and rabbit kittens <600 g only seasonally available, the Owl may have an insufficient prey base. The key to the Owl’s dietary needs may be a local diversity of small mammals (whether native, exotic or both); a limiting factor in its breeding distribution may be the availability of prey in the optimal size range for foraging males, which supply all the prey during critical phases of the breeding cycle (Schodde & Mason 1980). In the inland, the Owl may always have been restricted to high -nutrient sites such as chenopod shrubland near riparian woodland or caves, with a high mammalian prey base (cf. Morton 1990). Following overgrazing, the rabbit invasion and habitat clearance, the Owl may now be even more localised around remaining rich patches. The Masked Owl’s diet, and ability to hunt and breed in disturbed habitats, suggest that in coastal areas it is not the most threatened of Australian owls. In coastal habitats its prey, and hence the Owl, are not primarily dependent on old -growth (i.e. mature, undisturbed) forest although some mature trees are required (also Kavanagh 1992). Nevertheless, the Owl’s major native prey species require old -growth elements accumulated on the forest floor (Dickman 1991; Catling 1991); the results of Kavanagh & Bamkin (in press) on the Owl’s occurrence in the logging mosaic are of concern. The Masked Owl’s highest densities may now occur in certain unlogged drier forest types (also Mooney 1992, 1993). Its classification as threatened (Garnett 1992), and reclassification of the southern mainland race from “rare” to “insufficiently known” (Debus 1993a), is probably warranted until more is known of its biology and ecological requirements, and of any changes in its distribution and abundance in relation to agricultural clearing and other human activities. It may be secure on the coast and forested eastern edge of the tablelands, but threatened on the slopes, plains and far west. Fragmentation of the Owl’s inland distribution may be the forerunner of widespread regional extinction; in southern inland Australia, nominate novaehollandiae may indeed be the most threatened Australian owl taxon. S54 Debus & Rose Masked Owl October 1994 :The Masked Owl occurs in many state forests in eastern New South Wales, where surveys and research on large forest owls are in progress; it also occurs in conservation reserves. In forestry areas habitat will be permanently reserved around nest sites (R. Kavanagh pers. comm.), but it remains to be seen whether such protection will be fully implemented or effective. Peake et al. (1993) have made preliminary suggestions for research and management in forestry areas of Victoria, and these are applicable to NSW or are already being implemented and refined in the latter State (Kavanagh 1992). In eastern NSW the Owl’s conservation needs may be met partly by the status quo, with provision for age cohorts of trees to reach hollow- bearing age at intervals into the future. The availability of foraging habitat in wood -production forests may also need attention. Data on the Owl’s home -range size and habitat use in coastal forests are still required, using radio -tracking. In inland NSW, surveys are required to determine the Owl’s true distribution and habitat preferences, taking care to distinguish pale -breasted males from Barn Owls. In the inland the Owl may require additional habitat reserves, incentives for landholders to retain habitat and mature trees, rehabilitation of watercourse vegetation, and re-establishment of populations of native small mammals. Conservation issues have focussed on coastal forests at the expense of the semi -arid and arid zones; there are many habitat reserves in coastal forests and, where possible, many of those forests are being or will be managed sympathetically for owls and other wildlife. Conversely, the Masked Owl is poorly known in inland areas and more data are required. The significance of forest habitat, or conversely semi- cleared or arid habitats, for the Masked Owl remains to be determined. Drier and more open habitats, less suitable for the other large owls, have not been surveyed systematically for Masked Owls. Future research and management of the Masked Owl in New South Wales might profitably concentrate on the forests and woodlands on the inland side of the Dividing Range where, in the absence of the other two large forest owls, it is the top nocturnal avian predator. FOOTNOTE As this paper was going to press, two significant events occurred. One was the publication of Lunney et al. (1994), in which the status of the Masked Owl in western NSW was addressed. Schodde (1994) persisted with the view that the Owl does not occur in the Western Division, whereas Smith & Smith (1994) admitted the species for the Western Division on the basis of Sturt (1849) and Bennett (in North 1911). Furthermore, Smith & Smith classified the Owl as a “major decreaser” in the eucalypt woodlands of the arid and semi -arid zones. The second event was the completion of fauna surveys in state forests of the North-west Slopes in summer 1993-94 by E.M. Date and her colleagues for the Forestry Commission of NSW. Masked Owls were positively identified, by nocturnal playback and spotlighting, in eight state forests inland to Narrabri (Nandewar Range foothills), Pilliga (Pilliga West State Forest) and Coonamble (Sandgate SF), with unconfirmed records in four other state forests north to Yetman (Bebo SF) and south to Gilgandra (Breelong SF) and Dubbo (Beni SF), out of 27 state forests surveyed (E.M. Date pers. comm.; details in prep.). These records confirm our predictions on the Masked Owl’s occurrence on the western slopes, and illustrate the need for future surveys for this species in inland NSW. Australian Birds Vol. 28 Supplement S55ACKNOWLEDGEMENTS This paper has made use of the unpublished records and notes of many people. We thank the RAOU for access to Atlas records made by R. Gregory -Smith, J. Hardy, S. Marchant and P. Smith. NPWS field staff picked up road -killed owls (valuable distributional records), or sent pellet samples: D. Collins, P. Cope, I. Cranwell, R. Crombie, M. Harrison, L. McKenzie, R. Moffatt, M. Rogers, G. Vincent, S. Watts. We thank colleagues who provided owl records and notes: G. Beruldsen, C.J. Chafer, G. Clancy, G. Czechura (Qld Museum), F. Harrap, H. Hines, K. Holdsworth, G. Holmes, R. Kavanagh, T. Kenney, S.G. Lane, N. Maxwell, D. Morgan, T. Norton, D. Richards, A. Rogers, J. & N. Russill, M. Saxon, J. Skinner, L. Smith, D. Turner, V. Wright, and especially E.S. Hoskin for details in the Keith Hindwood Bird Recording Service. We thank John Disney, Belinda Gillies, and Richard Schodde & John Wombey for access to specimens and data in the Australian Museum, Museum of Victoria and Australian National Wildlife Collection (CSIRO, Canberra) respectively, and for facilitating museum work; also Jan Brazier (Aust. Museum Archivist) for A.R. McGill’s notes. Mark Adams, A.R. Parker, Bob McGowan and Mary LeCroy supplied details of Masked Owl specimens in the British Museum (Natural History), Merseyside Museum (Liverpool, UK), National Museums of Scotland, American Museum of Natural History and Academy of Natural Sciences (Philadelphia), respectively. Graeme Phipps supplied details of a Masked Owl at Taronga Zoo. David Read and the late Jack Mahoney assisted with literature, and Rod Kavanagh, Stuart Davey and Nick Mooney kindly provided advance copies of their unpublished papers with permission to quote them. Chris Chafer helped in the analysis of owl records. Dr Hugh Ford, Rod Kavanagh and Tony Norton commented helpfully on a draft, and comments by Alan Morris, Chris Chafer, Ian McAllan and Robert Payne improved the final version. Liz Date and State Forests of NSW kindly provided recent Masked Owl records for inland NSW, with permission to quote them. Appendix 1 Details of unpublished records of the Masked Owl in New South Wales, listed in approximately chronological order within the regions defined by McAllan & Bruce (1989). Excludes those listed in distribution text. AM = Australian Museum; QM = Queensland Museum; MV = Museum of Victoria; ANWC = Australian National Wildlife Collection, CSIRO, Canberra. Locality Comments North Coast: Raymond Terrace Specimen (AM 0.29987) collected in 1900. Orara River Specimen 4.8.1917 (MV: HLW 5310). Newcastle Specimen 28.12.51 (MV B4262). Male, 560 g; Rattus rattus in stomach. Belmont Road kill at Pelican 11.3.72 (K. Avery, A. Colemane, E.S. Hoskin). Bulandelah Specimen 9.6.73 (AM 0.44485): male, weight 453 g, wing 304 mm, span 1062 mm; two rodents (mice) in stomach. Road kill Mayers Ridge 19.11.84 (ABR): dry forest with rainforest gullies. Booral Road kill Karuah River 14.6.74: intermediate female, weight c. 800 g, wing 320 mm, wingspan 1137 mm, tail 157 mm, tarsus 78 mm, active wing and slight body moult, stomach contained Mus (?) (ABR). Open grazing land adjoining dry forest. (AM 0.5126). Karuah Male specimen 25.6.74 (AM 0.45220). Wallingat State Forest 20.12.77 one bird spotlit carrying a Sugar Glider Petaurus breviceps: it rose off a track with it and was followed for 0.5 km before it turned off into the forest (ABR). Dry forest ridge, near rainforest gullies. S56 Debus & Rose Masked Owl October 1994 :Singleton Bird spotlit 31.12.83 by I. Cranwell, 40 km N of town at 700 m altitude; fresh pellet under tree perch contained Hastings River Mouse Pseudomys oralis and juvenile Long -nosed Bandicoot Perameles nasuta (ABR). Dry forest. Gloucester Road kill 26.10.84 (ABR). Open grazing land, trees along road. Pacific Palms Bird caught on roadside barbed wire 17.6.85, kept until it could fly. Fed on Mus; 32 x 20 mm pellet contained 2 Mus skulls (ABR). Dry forest. Nana Glen Road injury October 1985: dark female, wing 345 mm, wingspan 1160 mm, restored to health and released (S.G. Lane). Alstonville Alphadale 1988: one bird regularly seen roosting in large Tallow – wood Eucalyptus microcorys in regenerating wet sclerophyll forest, on escarpment overlooking Tuckean Nature Reserve; sample of 5 pellets collected, sent October 1988 (B. Baigent, per R. Moffatt). Coffs Harbour Corindi area (?) 13.5.89, large tree blown over in high winds, hollow contained two chicks (one killed in fall), survivor taken to Kumbaingeri Wildlife Park by L. Casson. Mouse and rat in nest hollow. Chick downy with no mask. On 7.6.89 feathers showing through down, mask evident; on 26.6.89 almost fully feathered; on 12.7.89 fully fledged (J. Skinner). Mt Marsh State Forest One bird calling almost all night, seen by spotlight September 1989 (D. Pugh, per H. Hines). Coutts Crossing One bird on roadside post 20.3.89 and 3.3.90 (G. Clancy). Raymond Terrace Injured female sent via local vet to Taronga Zoo 9.8.91: weight 476 g when found (emaciated), 864 g (freshly fed?) 28.8.91 when recovering, 797 g 18.10.91; wing 329 mm (G. Phipps). Forster Lakes Way below Booti Hill, 4.5.92, bird flew low in front of vehicle 19:30 hrs (ABR). Central Coast: Liverpool Specimen (AM 0.9277) registered in 1897. Concord Specimen (AM 0.2359) registered in 1888. Cooks River Specimen (AM 0.14109) registered in 1905. Illawarra Specimen (AM 0.23634) registered in 1915. Wallacia Specimen (AM 0.29989) collected 18.10.1916. Cambewarra Bird killed on barbed wire fence 31.5.1933. “Mislaid” measurements of two juvenile males reported by Elliott (1935): total length 15″ (381 mm); wing from tip to body 17″, 18″ (432 mm, 457 mm); tail 5″, 5.25″ (127 mm,133 mm). Adult male found dead after foot injured by rabbit trap 4.5.1936. Juvenile heard calling 16.5.1938 (all A.J. Elliott unpubl. notes, per C.J.Chafer). Bomaderry Specimen collected before 22.4.1934, prepared by E. Read (A.J. Elliott unpubl. notes). Avalon One bird roosting under canopy of Cabbage Palm Livistona australis 29.9.1935 (K.A. Hindwood, per E.S. Hoskin). Ourimbah Specimen (AM 0.34892) registered in 1936. West Pennant Hills One bird roosting 8 m above ground in pine tree 9.2.60 (N. Feamley, K.A. Hindwood, per E.S. Hoskin). Newport Female specimen 10.6.65 (AM 0.41552). Mammal fur in stomach. Berkeley Two dark birds in Casuarina forest with Melaleuca understorey at Hooka Creek 1965; one collected as a specimen by a youth (L.E. Smith per C.J.Chafer). Pennant Hills Specimen 22.4.67 (AM 0.42261): female, weight 706 g, wing 330 mm, span 1075 mm. Road kill 7.9.72: male, weight 580 g, wing 307 mm, span 1080 mm (ABR; AM 0.44309). Dee Why Specimen 21.7.68 (AM 0.43004). Male, 425 g. Australian Birds Vol. 28 Supplement S57Kenthurst One bird found injured, died later, Glenhaven area 23.11.68 (K.A. Hindwood, per E.S. Hoskin). Primbee One bird in dune forest 1969 (L.E. Smith, per C.J. Chafer). Royal National Park Road kill Lady Carrington Drive 30.6.70 (L.McKenzie): dark adult female, weight 680 g, wing 330 mm, wingspan 1147 mm, tail 145 mm, tarsus 77 mm, slight body moult, stomach contained mammal whiskers (ABR). Wet forest. (AM O. 5041). Gosford Road kill Brisbane Water National Park 27.8.71: white -breasted male, weight 672 g, wing 305 mm, wingspan 920 mm, tail 134 mm, active body moult, 3 Mus musculus in stomach; dry forest and heath (ABR; AM 0.4977). The Entrance Road kill 3.1.74. Male, weight 364 g, wing 315 mm, span 1000 mm. (AM 0.44898). Homsby Recorded for the period 1966-1976 (E. Reynolds/Atlas). Gerroa Road kill Seven Mile Beach 25.2.80: female, weight 670 g, wing 330 mm, wingspan 1040 mm, tail 154 mm, tarsus 70 mm, active body moult, stomach contained Long -nosed Bandicoot (ABR). Blackbutt Eucalyptus pilularis open forest with Banksia understorey. (AM 0.55083). Asquith Ku-ring-gai Chase National Park 2.10.80, roosting bird flushed from rock overhang (I. Cranwell). Dry forest on sandstone. Winmalee One pale morph spotlit at night 1.1.81, dense wet sclerophyll forest in mountain gully (J. Hardy/Atlas). Mangrove Creek Near Mt White, north of Sydney 12.10.81, one bird observed carrying prey which it dropped: as the carcass was approached by torchlight, the owl came down and took it into a tree; the remains of a Long -nosed Bandicoot were found next morning (ABR). Wet forest. Peats Ridge Road kill 12.1.85 (AM 0.58671). Male, 450 g. Sydney city One bird Margaret Street [Wynyard Park?) 14.4.85 (J. Hardy, per E.S.Hoskin). Helensburgh One bird flushed in daylight from creekside vegetation, flew into adjacent forest, October (?) 1991 (D. Rayment per C.J. Chafer). South Coast: Ulladulla Road kill Higgins Creek 7.4.70 (K.A. Hindwood, per E.S. Hoskin). Batemans Bay Specimen NE of East Lynne 6.3.75. Male, 410 g. Open forest near palm gully (ANWC 17891). Moruya Road kill Tuross Heads 21.9.79 (S. Marchant/Atlas; AM 0.47735): female,wing 319 mm, span 1004 mm. Road kill 2 km N, March 1982: male, weight 445 g, wing 300 mm, wingspan 966 mm, tail 128 mm, Rattus sp. in stomach; woodland (ABR). Road kill 7 km S of town April/May 1991: forest/pasture interface; very open, with clumps of trees >100 m away; forest c. 1 km away (R. Kavanagh).
Bega Road kill Princes Hwy 29.9.79; dairy pasture with trees on fence -lines
(R.Gregory-Smith/Atlas). Road kill Bega-Cobargo 25.1.80, in pasture with
scattered trees and clumps of trees, km from forest: female, wingspan 1120
1
mm, heavy wing, tail and body moult, rabbit in stomach (P. Smith/Atlas).
Eden region Road kill 13 km S of town March 1992: open forest with some natural openings
near a swamp and river (M. Saxon per R. Kavanagh).
Northern Tablelands:
Barrington Skull of Masked Owl prey (Sugar Glider) sent to Aust. Museum by the late E.L.
Hyem of “Mentor (per J. Disney).
Coolah Tops Specimen found dead 20.8.76 (per NPWS): stomach contained vegetarian
mammal (ABR).
S58 Debus & Rose Masked Owl October 1994
:Yarrowitch Recorded breeding 1951-76 and 1977 (C.H. Young/Atlas).
Werrikimbe Natl Park Bird found dead Tobins Creek 8.10.80, appeared to have a bite or very thin
claws penetrated above the eye: female, weight 435 g (thin), wing 333 mm,
wingspan 1120 mm, tail 150 mm, tarsus 74mm, stomach empty ; wet forest
(ABR).
Tomalla Tops 27.9.82. bird caught up on barbed wire and died (VI Wright): female, weight
700 g, wing 330 mm, winspan 1130 mm, tail 150 mm, tarsus 73 mm, active body
moult, stomach empty (ABR). Open grazing land adjoining dry forest. (QM
0.22470).
Chaelundi State Forest Undated, recent (post -1970) sighting by M. Clayton (per T. Norton).
Tenterfield Road injury 1990, cared for until released (K. Holdsworth).
Glen lnnes One bird London Bridge State Forest 26.10.91: responded to tape playback with
loud cackle then screech; seen closely, in large logged clearing in eucalypt forest
(G. Holmes).
Central Tablelands:
Lithgow Specimen (AM 0.29988) collected in November 1901.
Moss Vale Female specimen June 1942 (AM 0.37577).
Mittagong June/July 1973: large, buff- faced bird roosting in daylight in tree on road verge.
in open country with well -timbered fenceline 1.5 km SW of town (F. Harrap).
Southern Tablelands:
Bombala Road kill 4 km W of Wyndham, between Eden and Bombala, 22.6.91: forest/
pasture interface near creek (D. Morgan per R. Kavanagh).
North-west Plain:
Baan Baa One bird seen February 1990 (D. Richards).
Wee Waa One bird seen in town, undated [recent, c. 1989?] (H. & B. Mannes. per D.
Richards).
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Appendices
Details of published records of the Powerful and Masked Owl in New South Wales. These are
individually available from the authors as an accessory publication. They are also lodged
with the NSW Field Ornithologists Club, the NSW Bird Atlassers and the Ornithology
Department, Australian Museum.
FOOTNOTE
Since this issue went to press, a paper was published on the Powerful Owl (Pavey 1994,
Sunbird 24, 30-39). That paper confirms the Powerful Owl’s wide dietary diversity; reliance on
Common Ringtail Possum, Petaurus gliders and fruit bats Pteropus spp. as prey in subtropical
lowlands, with Greater Gliders taken mainly in the highlands; and the ability of the Owl to forage
in regrowth forest and suburban gardens.
S64 October 1994Advice to contributors
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References to books appear in the form
Marchant, S. & Higgins, P.J. (eds) 1990, Handbook of Australian, New Zealand and Antarctic
Birds, Vol. 1, OUP, Melbourne.
and to journals as
Morris, A.K., Tyler,V., Tyler, M., Mannes, H. & Dalby, J. 1990, ‘A waterbird survey of the
Parramatta River wetlands, Sydney’, Aust. Birds, 23:3, pp. 44-64.
These are cited in the text as Marchant & Higgins (1990) or (Morris et al. 1990), respectively.Volume 28, Supplement AUSTRALIAN BIRDS October 1994
CONTENTS
Debus, S.J.S. General Introduction
1
Debus, S.J.S The Sooty Owl Tyto tenebricosa in New South Wales 4
Debus, S.J.S
& Chafer, C.J. The Powerful Owl Ninox strenua in New South Wales 21
Debus, S.J.S. The Masked Owl Tyto novaehollandiae in New South Wales … 40
& Rose, A.B.
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