Context-, phenotype-, and kin-dependent natal dispersal of barn swallows (Hirundo rustica)

Natal dispersal is a major life-history trait, with important consequences for population dynamics and genetic structure. Successful dispersal depends on a complex blend of decisions at all main stages of the dispersal process: emigration, prospection for a site, and settling. Costs and benefits of such decisions are expected to depend on sex and on the ecological context, on individual physiological state, and on concomitant decisions by relatives, which affect competition with kin and inbreeding. We analyzed natal dispersal propensity (i.e., dispersing or not) and dispersal distance in the semicolonial barn swallow (Hirundo rustica) in relation to context-, phenotype-, and kin-dependent factors. Females had larger dispersal propensity and distance than males. Dispersal propensity of both sexes was negatively density dependent and was less likely from colonies (farms) with large number of livestock, which is important to barn swallow distribution. Dispersal propensity was larger among males ranking high in the body mass brood hierarchy and smaller among late-hatched females. Dispersal distance was larger for late-hatched males and for females that ranked high in the body mass brood hierarchy. Finally, both dispersal propensity and distance of males increased with the number of male siblings. We, thus, identified several context-, phenotype-, and kin-dependent components of dispersal decisions. Phenotype-dependent effects suggest that decisions of whether to disperse and of dispersal distance are different processes under control of sex-specific traits. Finally, male dispersal behavior suggests that kin selection favors males that reduce the risk of sib–sib mating competition, in a population with male-biased tertiary sex ratio.