Population density and presence of the mother are related to natal dispersal in male and female Antechinus stuartii

In common with most mammals, the frequency of natal dispersal in antechinuses is strongly male-biased. Inbreeding avoidance has been put forward as the most likely explanation, with juvenile dispersal being driven by the mother. Dispersal distances and factors affecting emigration and immigration of each sex have not previously been studied in antechinuses, because of the difficulty of following the fates of individual dispersers. I studied a dense population of brown antechinuses (Antechinus stuartii) of known parentage in linear habitat that could be comprehensively trapped, and determined the fate of 27 females and 14 males that survived to dispersal age. Juvenile males dispersed not only more frequently than females (71% v. 11%), but also much further (maximum known distance: 1230 m v. 270 m). Males dispersed further if they had been raised in an area of low population density, and were more likely to immigrate into an area with a higher density of females than the natal site. Death of the mother disrupted normal home-range establishment, resulting in frequent philopatry of sons and dispersal of some daughters. Some females emigrated after young were weaned, and this also prompted dispersal of daughters. There was no evidence that daughters with surviving, philopatric mothers were more likely to survive to breed. I conclude that male-biased dispersal appears to result not only from costs of inbreeding, but also partly by the benefits of finding a site with more mating opportunities.