Philopatry or dispersal: competition for territory vacancies in the splendid fairy-wren, Malurus splendens

Abstract

Abstract. This study examines intra-sexual competition for territory vacancies and natal dispersal in the cooperatively breeding splendid fairy-wren resident near Perth, Western Australia. Observational data from a 17-year study were used to test several current hypotheses of natal dispersal. Demographic and environmental factors influenced dispersal within the cooperative social system and promiscuous mating system. Survival of breeding adults was high, and in most years the few available vacancies were in established groups; new groups were formed infrequently. Surplus males were always available for any vacancy that occurred; in some years, there were more vacancies than spare females. Birds of both sexes inherited the senior positions in their natal territory (61% of known males and 39% of females). Natal dispersal was female biased, but many birds of both sexes delayed dispersal and helped for 1 or more years in their natal territory before acquiring a senior position there or elsewhere. Few birds of either sex dispersed more than one territory away front their natal territory; more than 75% of males and females bred in their natal territory or an adjacent one. Vacancies for both males and females were filled by birds from outside the group only if no replacement was available from within; replacement was rapid during the breeding season with no overt competition, even though, in most cases, several non-breeding candidates were available in adjacent territories. Vacancies filled from outside the group were not always taken by the oldest available bird. Once past their first year, male helpers were more likely to stay in their natal territory, often eventually inheriting it; males rarely left groups in which they were the sole male helper. No synchronized pulse of post-fledging dispersal occurred, but some juveniles did disperse and wander. Most dispersal occurred in response to an obvious opportunity. No evidence of inbreeding avoidance was found and dispersal was unrelated to the lifetime reproductive success of males or females.