Study Finds Link Between Climate and the Size of Bird Bills

The size of a bird’s bill is linked to climate because of the role that bills play in maintaining body temperature, according to a new study. After examining 214 species of birds — including toucans, parrots, Canadian gamebirds, and penguins — researchers at the University of Melbourne and at Brock University in Canada found that birds with larger bills tend to be found in warmer climates, while birds that have to deal with colder climates have evolved smaller bills. “This suggests that there is an evolutionary connection between the size of the birds’ bills and their role in heat management,” said Matt Symonds, professor of zoology at the University of Melbourne and lead author of the study, published in the journal American Naturalist. While Symonds said it is possible that large bills evolved to get rid of excess heat to prevent overheating in the birds’ bodies, he said it is more likely that colder temperatures impose a constraint on bill size. The research, he said, affirms an ecological theory known as Allen’s rule, which predicts that appendages like limbs, ears, and tails evolve smaller in cold climates to limit heat loss.