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 migratory collared flycatcher, Ficedula albicollis, may be partly caused by age and sex differences in the balance between benefits of using prior local experience and costs of time devoted to finding the way home. To test this idea, newly arrived birds of different sexes, ages, prior local experience and arrival time were experimentally translocated between woodlands with nestboxes, about 1.5-6 km apart, and the return rates of different categories of birds were then compared. About 54% (N=230) of the displaced birds returned to the plot of capture compared with 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 yearlings, with experience of the plot of capture from the previous year were more likely to return than those with no such experience. Old males were more likely to return than old females, and males, but not females, of both age classes that arrived early were more likely to return than those that arrived late. It is concluded that the higher degree of philopatry of old birds is best interpreted in terms of increasing benefits of prior local experience with age. The significance of prior local experience may differ between sexes because of a difference between males and females in the costs of finding and comparing alternative nest sites, with the highest benefits accruing to the sex with the highest average search costs, that is, males in the collared flycatcher.