Natal and Breeding Dispersal in a Co-Operative, Extra-Group-Mating Bird

Natal and breeding dispersal of yearling and adult Superb Fairy-wrens Malurus cyaneus were studied for five years in Canberra, Australia. Superb Fairy-wrens are co-operative breeders and exhibit male philopatry and female-biased dispersal. Dispersal by yearling males was prompted mainly by breeding vacancies in nearby territories, and most males acquired a social mate without leaving their natal territory. All females dispersed in their first year, in two discrete phases. Early dispersal by females appears to be volitional, whereas late dispersal is forced by aggression by mothers. Early-dispersing females fledged earlier and dispersed further than latedispersing females. Females travelled further than males, and either gained a breeding position at age one year, or disappeared. Obligate dispersal by young females appears to be costly, contradicting predictions of philopatry by co-operative breeding theory. Dispersal by established breeders was uncommon, and was female-biased. The role of the unusual mating system of the species is discussed, and dispersal patterns in this species are compared and contrasted with those of its congener M. splendens.