SSS 2009-12-04（在线收听）

We usually think of evolution as something that happens over eons, in remote places where people rarely venture. Not something that happens around the backyard birdfeeder in just a few decades. But a study in the journal Current Biology suggests that feeding birds in winter can influence their course of evolution.

The birds in this study were central European blackcaps, a common kind of warbler. In spring, they breed in southern Germany. And when winter comes, they all fly south to the Mediterranean. At least they used to. In the 1960s, folks in Britain started putting out seed in winter. And the blackcaps split into two distinct groups. One goes to Spain to nosh on fruits and olives, the other heads north to take advantage of the easy English pickin’s.

The two populations may even be splitting into two species. The blackcaps that winter in England tend to mate with each other when they return to Germany. So they’re starting to look different from the birds that go south. Their beaks are longer and narrower, less suited to supping on Spanish olives. As birds of a feather, they definitely flock together. And to some degree, they have a bunch of bird-feeding Brits to thank.