Breeding Diet of the Australian Red Goshawk and its Implications for Understanding the Species’ Trophic Niche and  Decline

The Red Goshawk (Erythrotriorchis radiatus) is one of Australia’s least encountered birds, is poorly known, and under serious threat following its recent extinction in one-third of its historical breeding range, and population decline in another one-third of that range. The species is now confined to the tropical savannas of northern Australia as a breeding resident yet our understanding of its diet and trophic niche within these environments is limited. Using a comprehensive dataset of prey records, we found that Red Goshawks are specialized avian predators targeting specific prey such as Rainbow Lorikeet (Trichoglossus moluccanus), Red-collared Lorikeet (Trichoglossus rubritorquis), Blue-winged Kookaburra (Dacelo leachii), and Sulphur-crested Cockatoo (Cacatua galerita). These bird-eating habits likely require extensive home ranges and may explain why the species exhibits extreme levels of reverse sexual size dimorphism. We found that females hunted larger prey than males, and that the size of prey increased throughout the breeding season likely due to the female hunting later in the breeding season. The size and composition of prey appeared to be influenced by breeding habitat, with riparian areas apparently supporting higher prey diversity and larger prey size including waterbirds. Prey selection by Red Goshawks appeared specialized and not proportional to the relative availability of birds within the environment. Fledgling sex did not determine the size of prey delivered to nests despite the significant size discrepancy between male and female young. We also found that the prey species that Red Goshawks most depend upon appeared to remain abundant in the Red Goshawks’ former range areas. Consequently, the loss of prey populations did not appear to account for the species’ significant recent decline, although habitat loss and change may inhibit its capacity to hunt these prey items.