The Adaptive Zone of the Genus Gerygone (Acanthizidae) as Shown by Morphology and Feeding Habits

Abstract

Using body morphology, feeding ecology and behaviour, this paper describes the adaptive zone of the species-rich Australo-Pacific genus Gerygone. Gerygone is a genus of small bodied, specialist insectivores that obtain the majority of their prey by gleaning and snatching it from the foliage. Species tend to be ecologically and morphologically similar. Evolution has mainly taken the form of specialisation to different habitats, to produce a largely allopatric assemblage of species. In this it parallels the larger bodied, foliage-gleaning Lichenostomus honeyeaters and contrasts with other species-rich endemic warbler-like genera, such as Sericornis and Acanthiza, where sympatric species exploit different substrates, forage at different heights above the ground, and use different foraging behaviours. The greatest evolutionary shifts occur in the insular species, Gerygone igata and G. albofrontata, which are morphologically and ecologically distinct from other Gerygone. On the limited data available, it appears that the morphological radiation of Gerygone in Australia and New Guinea is constrained by the abundance of other insectivorous genera.