Breeding biology and social structure of White-winged Fairy-wrens (Malurus leucopterus): comparison between island and mainland subspecies having different plumage phenotypes

Abstract

White-winged Fairy-wrens have a clan mating system wherein up to three cooperative breeding groups (breeding pair plus any helpers) are contained within the larger territory of a nuptial-plumaged male who also has a mate (likely with helpers). Nuptial-plumaged males of island and mainland subspecies have different plumage phenotypes: in the mainland Australian suspecies (Malurus leucopterus leuconotus) nuptial males are blue with white wings, whereas in the subspecies on Dirk Hartog (M. l. leucopterus) and Barrow (M. l. edouardi) Islands males are black with white wings. Here, we compare island and mainland populations of White-winged Fairy-wrens in morphology, breeding biology and social behaviour based on data collected over two breeding seasons on Dirk Hartog Island and near Lancelin, Western Australia, on the mainland. In addition to the colour differences of the nuptial males, mainland males and females were significantly larger than their counterparts on the island and mainland birds had significantly higher realised reproductive success. Pairs on Dirk Hartog Island had significantly smaller clutches, longer incubation periods, decreased hatching success, and fledged fewer offspring. Moreover, most mainland pairs had 1–4 helpers at their nests, whereas island pairs had few, if any, helpers at their nest. Thus island birds could be characterised as largely socially monogamous, whereas mainland birds were mainly cooperative breeders. We discuss morphological differences in relation to general island-mainland patterns of avian body size and relate island-mainland differences in reproductive success and social behaviour to research on parental care and sexual selection in other fairy-wren species.