Tufted puffins (Fratercula cirrhata) possess large bills and are members of the bird family with energetically expensive flight. In a new study, a team of researchers from Canada and the United States used infrared thermography to test whether wild tufted puffins use their bills to dissipate excess heat after flight. The data showed that within 30 min of landing, the temperature of their bills dropped by 5 degrees Celsius (from 25 to 20 degrees Celsius), while the heat radiating from their backs hardly changed.
“Why would puffins have evolved such a large bill? We think it could have to do with the energy they use when they fly,” said Professor Kyle Elliott, from the Department of Natural Resource Sciences at McGill University.
Energetically speaking, flying is very taxing to birds. During flight, the thick-billed murre (Uria lomvia) — which is closely related to the tufted puffin — has an energy expenditure 31 times greater than when resting, the largest ever measured in vertebrates.
“This produces significant amounts of heat. Some birds evolved a large bill to help them cool down when they fly,” Professor Elliott noted.
“The avian bill is a classic example of how evolution shapes morphology.”
Thick-billed murres — and presumably puffins — produce about as much heat as a light bulb when they are flying.
“Our results support the idea that body heat regulation has played a role in shaping some bird beaks,” said Dr. Hannes Schraft, a postdoctoral researcher at the Université du Québec à Montréal.
“We think this also an example of exaptation, which means that an external structure is amplified to serve a new function; much in the same way the desert hare’s ears became bigger to help them cool down,” Professor Elliott added.
The scientists tried to figure out whether tufted puffins use their impressively large bills to dump extra body heat when they fly.
“We thought this might be the case because previous research has shown this to be the case in toucans and hornbills, bird species who also have very large bills,” Dr. Schraft said.
Because of its feathers, a bird’s body is very well insulated so thermoregulation can’t happen through sweating. Instead, the bill serves as a radiator when it needs to cool down — the equivalent of humans sweating on a hot summer day.
“This can seem counter intuitive. After all, when birds get cold, we often see them hide their beak in their feathers to stay warm,” Dr. Schraft said.
“Furthermore, biologists have demonstrated that on average, birds that live in cold climates have a smaller bill.”
Because the tufted puffins studied by the team live in Alaska, a smaller bill would have been, evolutionary speaking, the most logical outcome. However, competing needs might explain why puffins buck this trend.
“Overheating can be a big problem for seabirds who need to fly long distances to feed their chicks during breeding season,” Dr. Schraft said.
“Puffins may have been able to overcome this problem by evolving a larger bill.”
The findings were published online in the Journal of Experimental Biology.
Hannes A. Schraft et al. 2019. Huffin’ and puffin: seabirds use large bills to dissipate heat from energetically demanding flight. Journal of Experimental Biology 222: jeb212563; doi: 10.1242/jeb.212563