Differential dispersal costs and sex-biased dispersal distance in a cooperatively breeding bird

In most bird species, dispersal distance from the natal territory to a breeding territory is greater for females than for males. Two main hypotheses have been proposed to explain sex-biased dispersal: 1) it serves as an inbreeding-avoidance mechanism or 2) it is linked to a sex difference in resource-holding potential and territory establishment. Additionally, in species where individuals delay dispersal and become subordinates in a natal territory, differences in benefits of philopatry (e.g. territory inheritance, own reproduction) may also affect sex-biased dispersal. We show that in the group-living Seychelles warbler, Acrocephalus sechellensis, females disperse further to obtain a breeding position than males do. However, we found no evidence that female-biased dispersal distance can be explained by the above-mentioned hypotheses: further dispersal does not lead to less-related partners, both sexes defend and can inherit a territory, and subordinate females are more likely to obtain...