ИСТИНА

The view that migratory paths are ruled by inherited cue-responses would suggest that it takes many generations for selection to effect large-scale changes in migratory behavior. Barn Swallow is a common breeder throughout much of North America, and the vast majority of this population migrates to Central and South America for the northern winter. This species began breeding in Argentina in the 1980’s in an area that had formally been near the edge of the bird’s common wintering range, and the population continues to grow and spread from there. Population genetic data, as well as observations in breeding colonies, indicate that individuals of North American origin are still recruiting to the Argentinean breeding population. The long-distance migration patterns of the North American birds raise a very interesting question: Do the swallows breeding in Argentina have a migratory route and destination like their North American ancestors, migrating to North America (and potentially even breeding there?!) in the southern winter, or do they instead migrate like most austral migrants to northern South America for the winter? Earlier analyses of stable isotope profiles suggested the latter, but those analyses could not rule out a North American migratory destination. Data from geolocation loggers now conclusively demonstrate that the birds have a migratory pattern like most austral migrants: they spend the southern winter in northern South America. We will discuss the possible mechanisms that may have produced this rapid change and its implications for the evolution of migratory patterns in general.