Comparative Tests of Birds Support a Link between Sex-Biased Dispersal and Body Size

Abstract

Abstract Background: Natal dispersal is the movement of individuals from their birthplaces to their first breeding locations. Such movements constitute one of the most important events in the life histories of birds and other species and are usually biased such that one sex moves farther and/or more frequently. Methods: In this study, we compile published data for different dispersal and mass characters for the females and males of 92 bird species from 15 different orders. We use these published data to test the prediction, as derived from species-specific dispersal studies, that sex-biased dispersal is related to body size. Our tests rely on comparative methods and alternative dated trees that directly account for the phylogenetic non-independence of species and the uncertainties in their phylogeny inference. Results: Our comparative tests support the prediction of a link between sex-biased dispersal and body size. Specifically, we find that larger species have more male-biased dispersal, that the dispersal distance is increasing more rapidly in males than in females, and that the female and male dispersal distances are both positively correlated with their sex-specific body masses. Conclusions: Sex-biased dispersal is related to body size. However, it remains elusive as to what is the mechanism (i.e., social/behavioral or physiological/energetic) that underlies this link. Still, this link is important, because it highlights the related area of species-specific dispersal as a source of new characters, hypotheses, and approaches for determining the underlying forces of sex-biased dispersal.