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. Researchers compared the bills of over 200 species of birds across the globe and found that the temperature of the birds’ climates can explain 16 percent of beak size variation.
- In 2009, Canadian researchers learned that toucans can alter the flow of blood to their beaks at will, allowing them to either release heat or stay warm.
How the Heck:
- In the current study, researchers at the Smithsonian Migratory Bird Center studied the beaks of 1,380 sparrows living in tidal salt marshes. The ten species of sparrows that the researchers looked at came from across the U.S., had similar diets (mostly insects and grasses), and lived in similar habitats. The only major difference between the animals was the temperature of their home environments.
- The team found that the size of the sparrows’ beaks varied greatly depending on the average summer temperature of their marshes—some sparrows had beaks 90 percent larger than their counterparts living in cooler marshes. In all, the researchers found that differences in average summer temperatures accounted for up to 89 percent of the variation in sparrow beak size.
The Future Holds: Greenberg and his team are now studying thermal images to get a better understanding of how birds use their beaks to cool down.
Image courtesy of Dave W. / Flickr