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Why does Rudolph the reindeer have a red nose?

Male caribou in Alaska
Credit: Dean Biggins (U.S. Fish and Wildlife Service) - Wikimedia Commons
Male caribou in Alaska
Why does Rudolph the reindeer have a red nose?

Rudolph is the red-nosed reindeer. But why do we say he has a red nose? Is it a bioluminescence phenomenon, the way it is with fireflies?

A well-supplied nose

According to researchers, reindeer have a high concentration of blood vessels in their noses. In fact, the number of capillaries in reindeer nasal tissue is 25 percent higher than that found in humans. In addition, like certain other mammals, caribous don’t sweat. If they get too hot, for example when pulling a big sleigh, the blood vessels in their noses will dilate, thereby increasing blood flow at the surface and with it the loss of heat.

Furthermore, an infrared photo shows clearly that after intense exercise, the nose, like the fore and hind legs, is warmer than the rest of the body. This thermoregulatory mechanism allows for the maintenance of a constant body temperature. When the sleigh travels at high altitudes, the reindeer are exposed to very cold temperatures, which is another reason for keeping body temperature well regulated.

Adapting to the cold

If Rudolph has a red nose, a physiological adaptation to the cold is involved. In the far north, caribou are exposed to intense cold that easily reaches -40 or -50 C. Moreover, there are no trees to reduce the power of the wind and its chilling effect. When a reindeer breathes, cold air enters through the nose. There it gets warmed up by the strong blood flow before traveling to the lungs for a gas exchange. Otherwise the cold air could freeze the delicate lung tissues.

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