Niche Partitioning by Two Sympatric Goshawks in the Australian Wet Tropics: Ranging Behaviour

Abstract

Two medium-sized woodland hawks, the Grey Goshawk Accipiter novaehollandiae and the Brown Goshawk Accipiter fasciatus, are sympatric in the Australian wet tropics. Because females are considerably larger than males, the two species and sexes form a four-member guild. Typically, when similar raptor species occur together they partition resources. Radio-tracking was used to study habitat use and composition, and interactions between the Australian goshawks. Sample sizes were small and there was considerable individual variation. Nevertheless, there was evidence of niche partitioning according to home range size and overlap, habitat composition and habitat use. In general, both species frequented forests or woodlands and adjacent open country. Consistent with morphological, dietary and hunting differences, Grey Goshawks, especially the males, frequented closed forest types and Brown Goshawks more open habitats of woodlands, crops and edges. In the non-breeding season, females ranged widely and their ranges overlapped both inter- and intra-specifically, whereas those of males of each species tended not to overlap with males and females of either species. In the breeding season, home range overlap declined markedly between neighbouring pairs of the two species, and there was no overlap between the females. The two species have relatively small home ranges, attributable to their rich habitat. In turn, this may facilitate co-existence of two such similar-sized accipiters. Nevertheless, there was evidence of competition between the two most similar-sized members of the guild, the male Grey Goshawk and the female Brown Goshawk.