EGRU-blog

Sex-biased dispersal, i.e. that one sex (be it males or females) disperses more than the other, is common in many species. For example, in large mammals male tend to disperse while females stay put while in most bird species it’s vice versa. There are good reasons why one sex should disperse and the other should be philopatric (e.g. inbreeding avoidance). But why should, e.g., in birds the females disperse and not the males?

One reason would be that the benefits of staying home (philopatry) differ between the sexes. In many bird species, males are (mainly) responsible for setting-up the breeding territory (and selecting good ones) while females choose among males. Consequently, it may pay more for males to stay close to home because the ‘local knowledge’ about good territories is more important for them. The females could after all rely on male characteristics for selecting good mates (and thereby good territories).

While this hypothesis has been around for quite awhile there are few studies that have tested it, mainly because of the difficulties in obtaining the necessary data on dispersal distances and fitness. Again, we used the extensive data set on Siberian jays to address this question and found that – in accordance with theory – life-time reproductive success declined with dispersal distance in males but not in females. The complete story is more complex and interesting, so it may be worth having a look at the paper now published as OnlineFirst.

Gienapp P, Merilä J (2010) Sex-specific fitness consequences of dispersal in Siberian jays. Behavioral Ecology and Sociobiology in press