Scientists have used infra-red technology to investigate the remarkable thermoregulation abilities of emperor penguins in Antarctica. Images of the penguins revealed that the warm-blooded animals can have a colder surface temperature than the surrounding air.
"At first we were very surprised by this discovery," said Dr. Dominic McCafferty from the University of Glasgow who worked with French scientists that braved sub-zero temperatures to observe the birds at the breeding colony of Pointe Geologie in Terre Adelie.
The study, published in the Royal Society journal Biology Letters, found that the birds demonstrated a key principle in the physics of heat transfer. Dr. McCafferty explained that only the region around the birds’ eyes was above zero due to “extreme radiative cooling” by the birds’ plumage. The birds’ environment was key to the phenomenon because they lost a large amount of heat through radiation to the clear sky, where heat escapes rapidly from our atmosphere.
"The sky has a temperature that may be more than 20˚C colder than the surrounding air," Dr McCafferty told BBC Nature. The biologist described how a car parked in the open on a cold night demonstrates the same principle: “Usually you will find frost to have formed on the roof and windscreen only but the sides of the car often do not have ice as these sides do not ‘view’ the sky and therefore are radiating to relatively warmer surroundings.”
The penguins are known for their thick, insulating feathers - the equivalent of “two ski suits” according to Dr McCafferty who explained that the specialised structure of these feathers prevents the “dangerously low temperatures” from transferring to the birds’ skin.