Natal philopatry in passerine birds: genetic or ecological influences?

The degree of natal philopatry (the likelihood that individuals breed at or near their place of origin) can influence the extent of inbreeding in animal populations. Passerine birds have been cited as typically showing high natal philopatry, and natal philopatry has been proposed as an adaptation to promote optimal inbreeding. A review of published and unpublished studies of passerines showed that natal philopatry was typically low, so maintaining a high level of inbreeding appears relatively unimportant for such birds. Rather, natal philopatry appeared to be more strongly influenced by ecological factors. Migratory passerine exhibited low natal philopatry compared to resident passerines, as predicted if dispersal costs for young birds are an important determinant of natal philopatry. The erroneous view that natal philopatry for passerines is generally high has resulted from a reporting bias toward resident species that have sufficient natal philopatry to study. Natal philopatry was found to be evolutionarily labile; populations of the same species and pairs of closely related species that differed in their degree of isolation differed considerably in their degree of philopatry. Future studies of natal philopatry should consider both the ecological factors that could affect dispersal costs and the reporting biases that influence which data on philopatry tend to be reported.