Wildlife

Birds are shrinking - Study

Birds are getting smaller. So shows an analysis of migratory birds that died after colliding into buildings in Chicago and were collected as specimens for the Field Museum of Natural History.

David Willard, a Field Museum ornithologist, has measured the Windy City’s dead birds since 1978. Data from his calipers and scales reveal decades-long trends in bird bodies: Their legs, on average, are growing shorter. They have lost weight. Their wings are getting slightly longer.

These changes are present in nearly all of the species he measured, according to a study of 70,716 bird specimens from almost 40 years published Wednesday in the journal Ecology Letters. Morphing birds, Willard and his colleagues say, reflect a changing climate.

The study authors examined precipitation, vegetation and other factors that could contribute to bird size. They determined an increase in summer temperatures is the strongest predictor for smaller birds.