129 AUSTRALIAN FIELD ORNITHOLOGY 2011, 28, 129–132 Observations on the Raptor Community of the Pilbara Region of Western Australia A.J.G. SUTTON 157 Nawaday Way, Singleton, New South Wales 2330 (Email: [email protected]) Summary Fourteen species of diurnal raptor were observed during roadside surveys and nest searches of the Newman district, in the eastern Pilbara region of arid north-western Australia, in 1987–88. Breeding data (months in which nestlings were present) are presented for eight of these species, and dietary observations or pellet analyses are presented for five. Raptor community structure, particularly with respect to bird-eating falcons in various size-classes, appeared similar to that elsewhere in the arid zone. Introduction There has been only one detailed study of the diurnal raptor community in the Australian arid zone, in the south-west of the Northern Territory (Aumann 2001a–d). Otherwise, apart from historical annotated bird or raptor lists for parts of the arid zone, there has been one other study of diurnal raptors, in arid north- eastern South Australia (Falkenberg et al. 2000; Falkenberg 2011), and an anecdotal account of some of the raptors at sites also in arid South Australia (Debus et al. 2006). This paper presents the results of road-transect surveys and nest searches for raptors in arid north-western Australia, obtained during a study on the Grey Falcon Falco hypoleucos (see Sutton 2011). Study area and methods The study area was that part of the Pilbara region within a 100-km radius of Newman (23°21′S, 119°43′E), in the Ophthalmia Range off the eastern Hamersley Range in arid north-western Western Australia (see Sutton 2011 for further details and references). The raptor community around Newman was surveyed by means of road counts according to the methods of the Royal Australasian Ornithologists Union Bird of Prey Watch Scheme (Baker-Gabb & Steele 1999). Two routes were followed, once per month, usually on the same day each month, during 1987 and 1988; the routes were chosen to sample a wide range of habitats and vegetation types: one in a north-easterly direction from Newman (85 km) to the Fortescue River floodplain (riparian River Red Gum Eucalyptus camaldulensis and Coolibah E. coolabah woodland), and one in a southerly direction (70 km) into Mulga Acacia aneura woodland. Each transect took ~1.25 hours, at ~70 km/h, and started at 0700 h. (The data could not be retrieved for further analysis here.) Nest searches were also conducted around Newman in the 1987 and 1988 breeding seasons. Nestling raptors were banded with metal leg-bands (supplied by the Australian Bird & Bat Banding Scheme). Seasonal conditions preceding and during the study period were below-average rainfall for the years 1986 and 1987 overall, but average or above-average rainfall during four of the six months in the first half of 1987; and below-average rainfall for four of the six months in the first half of 1988 (notably January–February) and throughout June–November (Bureau of Meteorology data). The Fortescue River did not flow during the study period 1986–88. In addition to a natural waterhole in the river, there was surface water available at bores. AUSTRALIAN 130 SUTTON FIELD ORNITHOLOGY Table 1 Months in which raptor nestlings of banding age, i.e. nearly fledged, were found in the south-eastern Pilbara, north-western Western Australia, 1987 and 1988. Number under month = no. broods. Riparian areas (i.e. perceived Grey Falcon nesting habitat) were targetted during searches so the results are not an index of relative abundance. Species Apr. May June Aug. Sept. Oct. Nov. Black-shouldered Kite 1 Whistling Kite 1 2 1 2 3 3 1 Spotted Harrier 1 Nankeen Kestrel 1 Brown Falcon 3 Australian Hobby 4 Grey Falcon 2 Black Falcon 1 Results and discussion The diurnal raptor community of the Newman study area consisted of 14 species, as observed during road transects (no further data analysis possible) and nest searches: Black-shouldered Kite Elanus axillaris (one nest, two nestlings banded), Black-breasted Buzzard Hamirostra melanosternon (one nest), Whistling Kite Haliastur sphenurus (13 nests; 19 nestlings banded), Black Kite Milvus migrans, Brown Goshawk Accipiter fasciatus, Spotted Harrier Circus assimilis (one nest, three nestlings banded), Swamp Harrier C. approximans (rare winter visitor), Wedge-tailed Eagle Aquila audax (no active nests confirmed), Little Eagle Hieraaetus morphnoides (four nests), Nankeen Kestrel Falco cenchroides (two nests; four nestlings banded from one), Brown Falcon F. berigora (seven nests; six nestlings banded); Australian Hobby F. longipennis (six nests; seven nestlings banded), Grey Falcon (two nests; four nestlings banded: see Sutton 2011), and Black Falcon F. subniger (one nest, one nestling banded). As riparian areas (i.e. perceived Grey Falcon nesting habitat) were targetted during nest searches, the results are not an index of the relative abundance of raptors over all habitats in the region. Months in which nestlings were found for banding (Table 1) indicated that most species had advanced nestlings in spring (September–October), except for the Whistling Kite which had advanced nestlings in almost all months from April to November. These findings are consistent with existing information on the breeding chronology of these species in the arid zone and elsewhere (e.g. Marchant & Higgins 1993; Olsen & Marples 1993; Auman 2001d). The Swamp Harrier was observed in June, feeding on a Little Pied Cormorant Microcarbo melanoleucos on the Fortescue River. A single Black Falcon was observed once, taking a juvenile (flightless) Pacific Black Duck Anas superciliosa on the ground (April), and a pair bred (August–October) at a waterhole ~7 km from a Grey Falcon nest. Whistling Kite food remains (in Kite nests) consisted mainly of Budgerigars Melopsittacus undulatus, and Whistling Kite remains were found at a Little Eagle nest. Three pellets from a Kestrel nest measured 24–26 × 14–15 mm (mean 25 × 14.7 mm), and contained Budgerigar feathers, grasshopper (Orthoptera) fragments, fur from a small mammal, and seeds (i.e. Budgerigar crop VOL. 28 (3) SEPTEMBER 2011 Raptor Community of Pilbara Region, WA 131 contents). Six pellets from a Hobby nest measured 23–38 × 12–15 mm (mean 32.2 × 13.8 mm), and food remains included bird bones, a passerine foot, the legs of a possible stilt (Recurvirostridae), insect wing-casing, seeds (crop contents of prey), and leaves (presumably ingested accidentally). Dietary findings for two breeding pairs of Grey Falcons are presented elsewhere (Sutton 2011); these Falcons took mostly parrots and other small birds. The breeding raptor community around Newman was broadly similar to that in the south-west of the Northern Territory (cf. Aumann 2001a–d), and to that in arid South Australia (cf. Falkenberg et al. 2000; Debus et al. 2006; Falkenberg 2011). The limited dietary data for Newman suggest a similar raptor community structure in the arid zone of Western Australia, at least for sympatric small and medium-sized, bird-eating falcons (cf. Aumann 2001c). Ignoring the generalist Kestrel and Brown Falcon, which take some birds among a range of vertebrate and invertebrate prey, available weight data (Marchant & Higgins 1993; Debus & Olsen 2011; Schoenjahn 2011) suggest three size-classes of sympatric Australian bird-eating falcons: Australian Hobby, Grey Falcon, and Black Falcon + Peregrine Falcon, with Black and Peregrine similar in weight but ecologically rather separated (Olsen & Olsen 1986), e.g. Peregrine scarce and localised near cliffs in the arid zone, Black a ‘steppe’ species (Marchant & Higgins 1993; Olsen 1994; Debus et al. 2005; Debus & Olsen 2011; Debus & Tsang 2011). Acknowledgements The project was funded by the Mt Newman Mining Company. Thanks are due to Ian Falkenberg (South Australian Department of Environment & Natural Resources) for helping to initiate the project and find nests, climber Steve Butters and BHP environmental officer Ken Walker for their involvement in the project, Ron Johnstone (Western Australian Museum) for the pellet analysis, and David Drynan (Australian Bird & Bat Banding Scheme) for issuing the banding summary. Thanks go also to Tom Aumann, Jerry Olsen, Penny Olsen, Jonny Schoenjahn and an anonymous referee for helpful comments on drafts of the Grey Falcon paper (Sutton 2011), supplementary data from which are presented here. References Aumann, T. (2001a), ‘Habitat use, temporal activity patterns and foraging behaviour of raptors in the south-west of the Northern Territory, Australia,’ Wildlife Research 28, 365–378. Aumann, T. (2001b), ‘An intraspecific and interspecific comparison of raptor diets in the south-west of the Northern Territory, Australia’, Wildlife Research 28, 379–393. 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(2006), ‘The birds of Bulgunnia and Mulyungarie Stations in the pastoral zone of arid South Australia’, South Australian Ornithologist 35, 27–37. Falkenberg, I.D. (2011), ‘Aspects of the ecology of the Grey Falcon Falco hypoleucos in the South Australian arid zone’, Corella 35, 23–28.