New research on song sparrows offers a new take on bird-beak evolution that is more nuanced than earlier ideas based on finch studies.
A finch's beak evolves according to the size and shape of available seeds. That conventional wisdom is one of the most accepted facts in science—it has been proved again and again in research that began in the Galápagos Islands, and stretches from Charles Darwin in the 1830s through to the modern work of evolutionary biologists Peter and Rosemary Grant. Case closed—right?
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.