The Arctic circle will experience its coldest time of year this month, as the sun does not rise in the visible sky between October and March. Animals that live in this part of the world have developed many adaptations for living easily and comfortably in these extreme conditions.
Most arctic animals are either very small or very large. Small animals, like arctic foxes and arctic hares, easily burrow under snow and ice to create comfortable dens. Tight entrances and long passages help keep air trapped under a thick layer of snow that acts as insulation, minimizing contact with the much colder external air. Body heat from the den’s occupants warms the temperature even further. Large animals also use dens including ringed seals and polar bears.
Polar bear on ice pack by Christopher Michel, Jul 2015; Musk Ox by Malcolm Manner, Mar 2013; Moose & frozen sagebrush by Steven Robinson, Oct 2017
Larger animals have a high body volume to surface area ratio, as is found in the shape of a ball. Internal heat is generated relative to body volume, and it is lost relative to surface area. Large, tubby animals including polar bears, musk oxen, and moose generate lots of heat while losing very little. Other adaptations help maintain this balance of heat and loss.
Thick, hollow fur/hair traps air inside each strand as well as underneath its heavy layers. Paws are covered in thick fur for stability, grip, and warmth. Long, furry tails can be used as blankets to wrap around bodies and noses. Oil secreted from special glands coat outer layers of fur, hair, feathers, and skin protecting the animal from direct contact with freezing waters. In addition, oil repels water so that it quickly runs off when the animal is on land, keeping them dryer and less exposed to cold air wicking away body heat.
Polar bears, arctic foxes, walruses, seals, and musk oxen all have blubber, a thick accumulation of body fat just below the skin layer. This prevents cold from penetrating the body cavities that contain vital organs. It can also be utilized for energy for movement or to create additional body heat. Huddling is another method used to prevent cold from getting to the center of a mass. Used by musk oxen, arctic foxes, walruses, seals, and arctic hares, staying close with a large group is warm and comfortable.
Reindeer, also known as caribou, are known by their long noses. Air follows a twisty route through the nasal passage before reaching the lungs. Interior walls contain many blood vessels close to the surface that warm the passing air up to seventy degrees before it enters the lungs. Warm blood running through arteries from the heart distributes body heat. By the time it reaches an animal’s extremities, it has cooled and not much body heat can be lost. Reindeer have countercurrent vascular systems where veins containing cool blood returning to the body’s core run adjacent to arteries with warm blood. The colder veins absorb heat so the body core stays warmer.
Extremities are one body area where heat is easily lost and exposure to cold can be damaging or deadly. Arctic foxes and arctic hares have shorter ears, noses, limbs, and snouts than species in the same families living in temperate weather zones. Ringed seals lack any external ears. Musk oxen have short legs and tiny ears, as do polar bears. Many of these adaptations can be viewed in the wild, or at your local zoo. Natural history museums also have displays where we can learn about many cold-adapted species.