a shadow of their former selves

Songbirds in the US are getting smaller, and climate change is suspected as the cause. A study of almost half a million birds, belonging to over 100 species, shows that many are gradually becoming lighter and growing shorter wings.

This shrinkage has occurred within just half a century, with the birds thought to be evolving into a smaller size in response to warmer temperatures.

Dr Josh Van Buskirk of the University of Zurich, Switzerland and colleagues Mr Robert Mulvihill and Mr Robert Leberman of the Carnegie Museum of Natural History in Rector, Pennsylvania, US decided to evaluate the sizes of hundreds of thousands of birds that pass through the Carnegie Museum’s Powdermill ringing station, also in Pennsylvania.

But some species are losing more weight. For example, the rose-breasted grosbeak has declined in mass by about 4%, while the Kentucky warbler has dropped 3.3% in weight and the scarlet tanager 2.3%. The headline finding is that the body sizes of many species of North American birds, mostly songbirds, are gradually becoming smaller, says Dr Buskirk.

Heat Is Online – originally BBCNews.com, 13 Mar 2010