Evidence for long-distance dispersal in a sedentary passerine, Gymnorhina tibicen (Artamidae)

Australian magpies (Gymnorhina tibicen) are group-living birds found across much of mainland Australia. Adults commonly remain in a breeding territory until death. Young of the year either remain on the natal (birth) site or are forced by their parents to disperse. Observational studies in south-eas tern Australia suggest that most dispersing juveniles settle within 7 km of their natal territory. Therefore, despite potential for considerable gene flow (via flight), social organization predisposes magpies towards local po pulation structuring. In this study, we measured genetic variation at both nuclear (allozyme) and mitochondrial loci and found evidence of substantial gene now over very large distances (up to 1599 km). Thus, some juvenile ma gpies may disperse much greater distances than was previously thought. For mtDNA, geographic and genetic distance were strongly correlated, consistent with a pattern of isolation by distance. Therefore, although female gene n ow is substantial it is apparently geographically restricted over large dis tances, in approximately a stepping-stone fashion. We conclude that a stron g relationship between gene now and geographic distance can develop even ov er large distances if populations have experienced no major historical dist urbances to gene flow. (C 2001 The Linnean Society of London.