Not necessarily. Two new studies, led by Smithsonian Conservation Biology Institute ornithologist Russell Greenberg, strengthen a budding theory that beak size may also be an adaptation to regulate temperature and conserve water. "Very few people ever stop to think that maybe these birds actually need water," Greenberg points out.

Years ago Greenberg noticed that sparrows who live in freshwater-stressed salt marshes tend to have larger bills than their relatives who live just a few kilometers inland. Then, in 2009, he read that thermal imaging revealed that toco toucans lose as much as 60 percent of their body heat through their bills. That got him thinking that maybe birds evolve larger or smaller beaks based on their need to either shed or conserve heat.

Matthew Symonds, an ecologist at Deakin University in Australia, was one of the first to investigate the relationship between beak size and latitude (a proxy for climate). "One of the arguments that was being thrown at us," Symonds says, was that toucans have exceptionally large beaks, so the "radiator" phenomenon probably would not apply to most birds.