IF THE toco toucan had evolved in chilly Ireland, its impressive bill would have been much more modest. That鈥檚 the conclusion of researchers who say heat exchange can be added to diet and mate attraction as key drivers of bird beak size.
Last year Glenn Tattersall of Brock University in Ontario, Canada, found the toco toucan loses up to 60 per cent of its body heat through its beak.
Now he and , at the University of Melbourne, Australia, have compared beak length in 214 bird species with the annual minimum temperature of their native habitats. 鈥淔rom toucans to parrots to grouse to penguins, species that deal with colder temperatures have smaller bills,鈥� says Symonds.
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They isolated the importance of temperature by studying only female beak length and comparing species with similar diets living in different climates.
Averaged across all species, temperature explained 16 per cent of beak size variation (The American Naturalist, ). For gulls and penguins it accounted for 66 per cent and 43 per cent of the variation respectively.
