IInteractions between Australian Ravens and raptors in a pastoral area of New South Wales: Interspecific aggression and nest-site spacing

Abstract

This study, near Tamworth, New South Wales, investigated the interactions within a diurnal raptor and Australian Raven Corvus coronoides community. The Australian Raven (hereafter ‘Raven’) is an abundant breeding resident here, is the only corvid that breeds in the area, and is known to have a close association with many raptor species. It is known to interfere with nests, provide frequent harassment and decrease the breeding productivity of several nesting raptor species, yet few studies have been completed on this issue, and its significance remains unknown. The abundance of raptors and Ravens and diversity of raptor species were determined from weekly surveys along a fixed 60-km transect in autumn to late spring 2016. A negative association was found between raptor species diversity and Raven abundance. The density and distribution of active or potential raptor and Raven nests were also recorded along the transect: active raptor nests had significantly more active stick nests of other species (raptors and Ravens) nearby (within 500 m), whereas active Raven nests had fewer such active nests within 500 m. Intruding Ravens and Wedge-tailed Eagles Aquila audax elicited significantly higher rates of defensive interactions from nesting Black Falcons Falco subniger than did other diurnal raptor species; Ravens triggered the highest rate of response. An increased understanding of the factors responsible for shaping community structure is useful for the management of threatened species. The raptor assemblage around Tamworth includes five threatened species, at least four of which are known to breed there, making competition for nest-sites here worthy of research.