Infrared Images of Penguin
Infrared images reveal the 'cold coats' emperor penguins use to keep cosy. The outer surface of an emperor penguin is colder than the air around it. On average the surface is four to six degrees Celsius colder than the air. The only exposed parts that are warmer are the eyes, beak and feet
Penguins are endotherms, which means that they have the ability to keep their body temperature at constant levels even when the surrounding temperature is very different. To regulate the body temperature they need to prevent the heat loss to the surroundings and insulate themselves well.
Penguins can minimize heat loss by keeping the outer surface of their plumage below the temperature of the surrounding air. Scientists have discovered the unusual thermal properties of the penguin's plumage while studying the birds in their natural environment using infrared imaging. During their research period, the average air temperature was 0.32 °F. At the same time, the majority of the plumage covering the penguin's bodies was even colder: the surface of their warmest body part, their feet, was an average 1.76 °F, but the plumage on their heads, chests and backs were -1.84, -7.24 and -9.76 °F respectively. Overall, nearly the entire outer surface of the penguin's bodies was below freezing at all times, except for their eyes and beaks. By keeping their outer surface below air temperature, the birds might paradoxically be able to draw very slight amounts of heat from the air around them. The key to their trick is the difference between two different types of heat transfer: radiation and convection.
The penguins do lose internal body heat to the surrounding air through thermal radiation, just as our bodies do on a cold day. Because their bodies (but not surface plumage) are warmer than the surrounding air, heat gradually radiates outward over time, moving from a warmer material to a colder one. To maintain body temperature while losing heat, penguins, like all warm-blooded animals, rely on the metabolism of food. The dark colored plumage of a penguin's dorsal (back) surface absorbs heat from the sun through radiation and help the penguins to warm up.
Since their outer plumage is even colder than the air, they might gain back a little of this heat through thermal convection — the transfer of heat via the movement of a fluid (in this case, the air). Heat exchange by convection depends primarily on the temperature difference between the skin and the air and on air movement. As the cold Antarctic air cycles around their bodies, slightly warmer air comes into contact with the plumage and donates minute amounts of heat back to the penguins. Then cycles away at a slightly colder temperature.