The marsh-loving song sparrow uses its beak to stay cool.

What’s the News: Scientists have long known that the size and shape of a bird’s beak is largely dependent on its diet. A hummingbird’s long, thin beak, for example, allows it to reach deep down into a tubular flower to get nectar. But in a new study in the journal Ecography, scientists have found that birds in warm climates have evolved beaks larger than their cooler-climate counterparts as a means of staying cool (birds, like most animals, don’t sweat). The new study adds weight to past research suggesting the same thing.

What’s the Context:

Allen’s Rule, a scientific theory coined by zoologist Joel Asaph Allen in 1887, states that warm-blooded animals will have longer appendages in hotter climates than those living in colder climates. The greater surface area allows the animals to give off more heat and keep cool.
A study last year showed that the rule may apply to birds’ beaks, too. ...