Habitat segregation and the insular syndrome in two congeneric raptors in New Caledonia, the White‐bellied Goshawk Accipiter haplochrous and the Brown Goshawk A. fasciatus

Abstract

The comparative distribution and abundance of the two congeneric goshawks of New Caledonia, the White‐bellied Goshawk Accipiter haplochrous and the Brown Goshawk A. fasciatus vigilax, were studied on 100 1‐km2 sample quadrats spread randomly over the island. The White‐bellied Goshawk is a well‐differentiated endemic forest‐dwelling species, presumably of older origin than the morphologically little‐differentiated island subspecies of the Brown Goshawk, which is restricted to open habitats. The two species exhibit ecological characteristics attributed to the so‐called insular syndrome; these characteristics were more pronounced in the White‐bellied than in the Brown Goshawk. The densities of both species were much higher than any density of the same or similar species ever recorded on a continent. Their habitat and foraging niches were broad. The two species were clearly segregated by habitat, their distribution overlapping only in semi‐forested lowland areas where the White‐bellied tended to encroach more on the habitat of the Brown Goshawk than the reverse. Possible determinants of their abundance, niche breadth and interspecific segregation are discussed, as well as the consequences for their conservation. The occurrence in New Caledonia of two additional congeneric species recently extinct and the existence of three other pairs of congeneric bird species with similar relationships are also emphasized.