THE IMPORTANCE OF LOCAL FAMILIARITY AND SEARCH COSTS FOR AGE-BIASED AND SEX-BIASED PHILOPATRY IN THE COLLARED FLYCATCHER

It is hypothesized that age- and sex-biased philopatry in the migrator y collared flycatcher, Ficedula albicollis, may be partly caused by ag e and sex differences in the balance between benefits of using prior l ocal experience and costs of time devoted to finding the way home. To test this idea, newly arrived birds of different sexes, ages, prior lo cal experience and arrival time were experimentally translocated betwe en woodlands with nestboxes, about 1.5-6 km apart, and the return rate s of different categories of birds were then compared. About 54% (N=23 0) of the displaced birds returned to the plot of capture compared wit h 86% of the controls (i.e. birds caught and released in the same plot ; N=79), suggesting that home area infidelity might be at least partly caused by high costs of finding the way home. Among displaced birds, older birds returned more often, and more quickly, than did yearlings, also when date of arrival was controlled for. Older birds, but not ye arlings, with experience of the plot of capture from the previous year were more likely to return than those with no such experience. Old ma les were more likely to return than old females, and males, but not fe males, of both age classes that arrived early were more likely to retu rn than those that arrived late. It is concluded that the higher degre e of philopatry of old birds is best interpreted in terms of increasin g benefits of prior local experience with age. The significance of pri or local experience may differ between sexes because of a difference b etween males and females in the costs of finding and comparing alterna tive nest sites, with the highest benefits accruing to the sex with th e highest average search costs, that is, males in the collared flycatc her.