SINGAPORE (Reuters) - Birds use their bills to regulate body heat, meaning climate plays a role in the size of their beaks, scientists say.
Scientists from the University of Melbourne in Australia and Canada's Brock University, examined bill sizes of birds from around the world and found that birds with larger bills tend to be found in hot environments.
Those living in colder climates had evolved smaller bills.
"Unlike humans they don't sweat but can use their bills to help reduce their body temperature if they overheat," said Glenn Tattersall of Brock University. The study of 214 species, from toucans and tinkerbirds to Australian parrots and Canadian gamebirds and gulls, showed that maintaining body temperature might have shaped the evolution of bird bills, in addition to their role in feeding and luring mates.
Thermal imaging of toucans and geese, for instance, show they can lose a large amount of heat through their bills.
"Across all species, there were strong links between bill length and both latitude, altitude and environmental temperature," Matt Symonds, of the University of Melbourne, said in a statement on Wednesday.
"This suggests that there is an evolutionary connection between the size of the birds' bills and their role in heat management," he said of the study published online this week in the journal American Naturalist.
The research validates a 133-year-old ecological theory called Allen's rule, which predicts that appendages such as limbs, ears and tails are smaller in cold climates to minimize heat loss.
"This is the first rigorous study of its kind to test this theory and to show that bird bills have evolved in this manner," Symonds said.
(Reporting by David Fogarty; Editing by Sanjeev Miglani)
