Swallows track human moves

Most studies of the impact of humans on other species tend to be negative as more and more habitats are destroyed or degraded, so a new study provides a surprising contrast. It adds weight to the view that one of the northern hemisphere's best-loved summer visitors has vastly increased in range and numbers as a result of human activity. The barn swallow is found across North America, Europe and northern Asia during the summer, where it has switched from ancestral nesting in caves to an almost exclusive preference for human structures. And in a new study by reporting in the Proceedings of the Royal Society (published online), the team has examined mitochondrial and nuclear DNA of modern birds to glean the birds' population histories. The birds were thought originally to have nested in caves, a resource extremely limited in availability, but evidence suggests they began to adapt to nesting in human structures beginning around 300 years ago. It is believed North American birds began attaching their nests to native American teepees in the early 1800s and that birds in Europe began to use structures and bridges in European settlements subsequently. The spread of humans across north America is thought to have resulted in a dramatic population expansion across the continent. Using DNA sequence analysis, the team find that mitochondrial DNA clades correspond to different populations in Europe, Asia and North America. But they also identified a clade associated with the Baikal region of Russia, distinct from the neighbouring Asian clade. Analysis of a sex-linked nuclear gene failed to throw light on the mitochondrial DNA results, suggesting that Features A new study maps the remarkable success of one bird species onto human activity, but one surprising Asian finding may predate recent human developments. Nigel Williams reports. Home on the range: A barn swallow nests readily in a barn structure in Kansas. (Photo: Larry Miller/Science Photo Library.) these main clades had evolved recently. Unexpectedly, the analyses show that barn swallows from North America colonised the Baikal region in the recent past. This dispersal direction is opposite to the direction for most changes in distribution between North America and Europe and Asia. Although this invasion was thought to coincide with the appearance of new types of human dwelling in the Baikal region, where until the nineteenth century most inhabitants lived in underground dwellings, calibration of molecular divergence suggests an older appearance of these …