The puffin’s iconic orange bill might be its most recognizable feature, but it’s also quite functional, serving the charismatic seabird in all avenues of life. The bill’s large volume makes it a hefty food carrier, and its ultraviolet glow amps up puffins' sex appeal. Now, scientists have identified yet another use of this dramatically curved bill: staying cool.

In a study published last month in the Journal of Experimental Biology, scientists found that big bills help the Tufted Puffin release excess body heat after an energetically demanding flight. This ability to dissipate heat has previously been studied in birds that live in warm climates, such as the Toco Toucan and the Southern Yellow-billed Hornbill. But while those birds use the numerous blood vessels in their jumbo-size beaks to keep from overheating in hot temperatures, the Tufted Puffin uses its beak to cool down after a high-intensity workout. Just like humans sweat, birds also need a way to maintain functional body temperatures.

“The puffins work exceptionally hard when flying, so this got us thinking about the potential role of the bill in dissipating heat,” says Kyle Elliott, an ornithology professor at McGill University and one of the study’s researchers. “When flying, they’re like a 100-watt lightbulb—that’s how hot they are—so they have to be able to dissipate that heat.”

Until now, no one knew that birds found in colder habitats, like Tufted Puffins in Alaska, use their beaks to regulate their internal heat. “It’s fascinating that nobody had yet looked at how large beaks work in colder climates,” says Tanja van de Ven, a researcher at South Africa’s University of the Witwatersrand who conducted a similar study on hornbills. “I’m pretty sure this is the first study that actually looks at the relationship between size of beak and cost of flight.”

To do the research, Elliott and his research team spent nearly one month in the summer of 2018 on Middleton Island, Alaska, observing Tufted Puffins on their nesting grounds. They recorded the birds with a thermal imaging camera, which visualizes heat in the form of infrared light, to capture bill and body surface temperatures; heat glows brightly in the resulting images. For each bird that landed within the camera’s field of view, the scientists took images approximately every two minutes until the bird flew away or entered a burrow. They ended up capturing more than 170 images of 50 independent landings.

The need to cool down after a rigorous exercise session could help explain why the puffin—a bird that is not the greatest flier—has such a large bill.

“The images showed that the bill lights up when the puffins land, which suggests that the birds are actively using the bill to dissipate heat,” Elliott says. Despite making up 6 percent of the body’s surface area, the bill was responsible for 18 percent of total heat exchange at landing, their calculations showed. This proportion decreased significantly with time, reaching 10 percent a half hour after landing.

These findings suggest that the need to cool down after a rigoruous exercise session could help explain why the puffin—a bird that is not the greatest flier—has such a large bill.

“It’s something I hadn’t really thought about because my focus has always been to look at these really colorful, ornamented bills as a trait used in mate selection,” says Heather Major, a professor at Canada’s University of New Brunswick who studies puffin-bill coloration. “It’s really interesting that these bills might also have physiological reasons for being that large, and to think about what came first—the size or the ornamentation.”

Finding a mate is important, but in order to breed and raise young, a Tufted Puffin needs to be able to find enough food for itself and its chicks. Its heat-dissipating bill helps with this, as it allows the birds to travel farther in search of food without having to take regular breaks to rest and cool down. This idea lines up with what we know about other cold-water seabirds: Among birds in the alcid family, the scientists write in their paper, large-billed species like puffins and razorbills have larger foraging ranges than smaller-billed murres.

“Other species like murres that have relatively small bills are actually at risk of mortality during breeding due to overheating, despite being an Arctic species in a cold environment,” Elliott says. “This is perhaps an important finding about how birds are going to respond to climate change.”

Next, the scientists hope to further research how these small-billed Arctic species like murres, which people don’t usually think of as being affected by thermal stress, adapt to changing temperatures between seasons. The scientists also aim to document the development of puffin bills to understand how thermal properties may change with age. Who knows what other fascinating discoveries about puffins’ overachieving, multi-functional orange bill they might make along the way.