Co-operative breeding in the superb fairy-wren, 'Malurus cyaneus'

Abstract

A population of Superb Fairy-wrens was studied from September 1982 to February 1986 at Eastwood State Forest, near Armidale, New South Wales. An attempt was made to investigate the adaptive significance of co-operative breeding in this population. Co-operative breeding arose when immature birds failed to disperse from their natal group and remained, instead, as non-breeding helpers for one or more years. Helpers assisted in the reproductive efforts of the breeding pair by feeding nestlings and dependent fledglings. ... The results of this study suggest that more than one type of ecological constraint may prevent fairy-wrens from breeding independently. In particular, males and females may be subjected to different types of constraint on independent reproduction, and may therefore delay dispersal for different reasons. Similarly, different constraints may operate in different years. Co-operative breeding in fairy-wrens was therefore seen to be an adaptation which maximised the fitness of breeders, and their offspring, when the reproductive opportunities for potential breeders were constrained.