Climate change makes birds shrink in North America

A study of almost half a million birds, belonging to over 100 species, shows that many are gradually becoming lighter and growing shorter wings in North America and climate change is suspected for this change. 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. However, there is little evidence that the change is harmful to the birds. In biology, there is a general rule of thumb that animals tend to become smaller in warmer climates: an idea known as Bergmans Rule. The scientists examined the records of 486,000 individual birds that had been caught and measured at the ringing station from 1961 to 2007. Their sample included local resident bird species, overwintering species, and even long distance migrants arriving from the Neotropics. Of 83 species caught during spring migration, 60 have become smaller over the 46 year study period, weighing less and having shorter wings. Of the 75 species migrating in autumn, 66 have become smaller.