Emperor Penguin Cloaks Play a Physiological Trick
In the northern hemisphere, winter is in full swing and snow has begun to accumulate in many cities. If you think braving the icy wind to get your driveway cleared of snow is a challenge, consider the struggles of the Emperor Penguin. Emperor Penguins not only survive the Antarctic winter, during which temperatures drop well below freezing and winds whip to gale-force speeds, but manage to complete their breeding cycle in this incredibly harsh environment. The amazing abilities of these birds to survive extreme conditions has been well documented by scientists and filmmakers. Nevertheless, there is still more to learn. A recent study by Dr.Dominic McCafferty of the University of Glasgow and colleagues in France showed that Emperor Penguins actually drop their surface temperatures below air temperature and get a sneaky benefit from doing so.
Penguins need to stay warm to survive, and also to incubate their eggs and warm their hatchlings. Thus, their core body temperature stays at about 37C (about 98F), in part due to their system of counter-current heat exchangers. While the core stays warm, however, temperatures at the extremities can plunge – in effect the penguins “turn off” heat flow to the flippers and feet to minimize overall heat loss. In the study, researchers used infrared imaging to measure the temperature of penguins in a breeding colony and find out how different parts of the body surface varied in temperature. During the measurements, air temperatures were a bone-numbing -17.6C (0 F). Unsurprisingly, the warmest parts of the penguins in these images were the eye and beak region and the flipper, which are two regions that are not wrapped in thick blubber (or lined with feathers, in the case of the beak). The rest of the body offered a surprise though – much of the penguin’s surface dropped below the ambient air temperature! In fact, many regions reached levels below freezing. The team concluded that this paradox may serve a useful purpose. Penguins are constantly losing heat through radiative heat transfer because their core temperature is so much higher than the surrounding temperature. They slow this process through the insulating effects of blubber and feathers, and by huddling with other penguins, and also burn the fuel of stored fat to generate metabolic heat. Heat can also be transferred by convection, and this is where the sub-zero plumage comes into play. Heat can be harvested by convection from any air that is warmer than the plumage. As the Antarctic air swirls around, packets of air that are above the plumage temperature will sometimes come in contact with the penguin and in these cases the features can absorb a bit of the difference. The amount of heat gained by this phenonomen appears to be very small, but in extreme environments every bit helps.
McCafferty DJ, Gilbert C, Thierry AM, Currie J, Le Maho Y, Ancel A. 2013. Emperor penguin body surfaces cool below air temperature. Biology Letters 9: 20121192.