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 inbreedi ng 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 A review of published and unpublished studies of passerines showed that natal philopatry wa s typically low, so maintaining a high level of inbreeding appears rel atively unimportant for such birds. Rather, natal philopatry appeared to be more strongly influenced by ecological factors. Migratory passer ines exhibited low natal philopatry compared to resident passerines, a s predicted if dispersal costs for young birds are an important determ inant of natal philopatry. The erroneous view that natal philopatry fo r passerines is generally high has resulted from a reporting bias towa rd resident species that have sufficient natal philopatry to study. Na tal philopatry was found to be evolutionarily labile; populations of t he same species and pairs of closely related species that differed in their degree of isolation differed considerably in their degree of phi lopatry. Future studies of natal philopatry should consider both the e cological factors that could affect dispersal costs and the reporting biases that influence which data on philopatry tend to be reported.