Ecology of raptors in the Canberra region, Australia

Abstract

We studied the general ecology of the Raptor Community living in the Canberra Region. In particular, we were interested in the productivity, reproductive success, food habits and trophic structure. We located 12 species of breeding raptors in the area, similar to previous surveys. Although we located most nests on farmland and non-urban nature reserves, there were 11 species were breeding inside the city limits, with the only exception being the White-bellied Sea Eagle Haliaeetus lellcogaster. a species that is mainly coastal but is also a breeding resident in this inland region, nesting in rivers and dams. The productivity and reproductive success of the community was high overall, with five species showing higher productivity than average, while four more had average productivity. Only two species had low breeding success and productivity. The Collared Sparrowhawk Accipiter cirrocephalus - who made breeding attempts but failed in most of them - and the Black-shouldered Kite Elanus axilaris - whose territories were inactive the first 18 months of survey. and only started breeding late in 2003. The diet of the raptors was similar to previous records, though there were exceptions. This study provided the first account of the food habits of inland Whitebellied Sea eagles. This species captured prey of aquatic origin, like the Australian Wood Duck Chenonettajubatta (23.3 % of items and 26.1% biomass); fish (23.3 and 26.1%) and reptiles (13.3 and 13.2%). The diet of the Brown Goshawk Accipiter gentilis showed an unusually high number of insects (54.4%), but birds and mammals provided most of the biomass. The dietary overlap (based on the Pianka index) of the species was low compared to other studies. The trophic structure produced by the UPGMA cluster analysis revealed 3 main feeding guilds: a) Vertebrate-feeders: Wedge-tailed Eagle Aquila audax, Little Eagles Hieraaetus morphnoides and Whistling Kite Haliastur sphenurus, which based their diet on mammals and large birds; b) Insect-small vertebrates guild: formed by the Brown Falcon Falco berigora and the Brown Goshawk; and c) Insect-feeders; Composed by the Nankeen Kestrel F. cenchroides and the Southern Boobok Ninox novaeseelandiae. The other five raptors were not grouped on any guild. Two of them were very specialized predators, the bird-catcher Peregrine Falcon F. peregrinus and the rodent-catcher Black-shouldered Kite. Finally, we explored some case studies on the topic of trophic dynamics. Two were comparisons of the diet of the same species living in the same area at different times. They provided contrasting examples of prey-switching. Peregrines and Hobbies adjusted to a decrease in the abundance of their main prey, the Starling Sturnus vulgaris, by consuming small numbers of several native bird species. Interestingly, it seems that the Starling decline is related to an increase of Common Myna Acridotheres Iris/is, a species that neither falcon seems able to capture. On the other case Wedge-tailed Eagles changed from a diet dominated by rabbit to a diet dominated mainly by other species: Eastern Grey Kangaroos (Birds as a group were also important),thus switching one prey species with another, unlike the falcons. On the final example, we used an original approach to evaluate the dietary overlap of two species (Wedge-tails and Sea Eagles) by clustering neighbouring pairs, which are more likely to show interspecific interactions. The neighbouring pairs showed low overlap in their diets despite their close proximity.

Date of Award	2005
Original language	English