Diet of 25 sympatric raptors at Kapalga, Northern Territory, Australia 1979–89, with data on prey availability
| Posted: |
12/12/2014 |
| Author(s): |
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This study describes prey availability and the diet of 25 sympatric diurnal and nocturnal raptors over 11 years 1979–89 in tropical Australia, at Kapalga in Kakadu National Park. Rainfall is seasonal: most falls from January to early March, resulting in pronounced annual wet and dry seasons. The major habitats include tidal rivers, seasonally inundated floodplains, upland open forests and woodlands, seasonal and permanent streams, and billabongs. About 365 vertebrate species have been recorded at Kapalga including Magpie Geese Anseranas semipalmata and many other waterfowl, Dusky Rats Rattus colletti and other small mammals, aquatic reptiles, frogs and invertebrates on the floodplains of the two tidal rivers. Sixteen raptor species were recorded breeding at Kapalga and another ten species were recorded breeding elsewhere in the Top End of the Northern Territory. Whistling Kites Haliastur sphenurus, the most numerous raptor at Kapalga, mostly breed on the edge of the floodplains, with nest densities up to seven nests per square kilometre. Magpie Geese were a major prey for many raptors, and adult populations up to 70 000 were available annually, as well as eggs (up to ¼ million) and flightless young during their late wet-early dry season breeding period. Dusky Rats were also a major prey species and their populations fluctuated between highs (up to ½ million) and lows on a 2-year cycle. Other prey including small mammals, snakes, frogs and insects greatly increased in numbers in response to increased dry-season vegetation on the floodplains after Swamp Buffalo Bubalus bubalis were removed about midway through this 11-year study.
Raptor dietary records were based mainly on pellets and prey remains collected at roosts, nests and feeding sites; and also on observations of prey hunted and captured by adult raptors. In total, prey identified comprised at least 49 bird species, 18 mammals, nine reptiles, eight fi sh, seven invertebrates and one frog. For the ten well-studied raptor species (≥20 diet samples), the major prey types of the Whistling Kite, Black Kite Milvus migrans and Black Falcon Falco subniger were mammals and birds; mammals and invertebrates for the Barking Owl Ninox connivens; mammals for the Rufous Owl Ninox rufa, Eastern Barn Owl Tyto javanica and Eastern Grass Owl T. longimembris; birds for the Red Goshawk Erythrotriorchis radiatus; and reptiles for the White-bellied Sea-Eagle Haliaeetus leucogaster and Brown Falcon Falco berigora. These diets were generally similar to those reported for these species elsewhere in Australia, although the Black Falcon took more rats than birds at Kapalga, and the Barn Owl and Grass Owl had a narrower food niche (rats only) than elsewhere.
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