The temperature drops, the water freezes, and the snow slowly drifts down. You and I bundle up and curl up with a nice mug of hot cocoa. But what do animals do when the mercury drops way below freezing? Many animals have developed some amazing adaptaions to deal with some nature’s most extreme conditions. This includes changing colors, growing extra fur and feathers, becoming dormant, and even taking advantage of the snow pack for warmth and shelter.
There are a number of animals that change from gray or brown to white in winter. According to Encyclopedia Britannica, color changes are thought to be linked to the amount of daylight, as temperature and location does not seem to affect it. In the case of the Arctic hare, mountain hare, and snowshoe hare, there are receptors in the retina that transmit information to the hare’s brain that stimulate the color change. There are also three species of weasel- the least weasel (Mustela nivalis), the longtailed weasel (M. frenata), and the shorttailed weasel (M. erminea) that change and this takes place regardless of temperature or location. In addition, Siberian hamster, the only domesticated animal to do so also changes regardless other environmental conditions. While changing coats has obvious camouflage advantages, there is also a theory that a pale coat may have better insulating properties as melanin, the substance responsible for a colored coat is absent, thus leaving more room for air spaces in the hair shaft. In ptamigans, there are air bubbles in the winter feathers, which also may help with insulation and also makes them appear brighter.
Another adaptation is dormancy in its various forms. In reptiles, this is referred to as brumation and this is induced by low temperatures. Brumating reptiles may move to drink water, but they can go months without food. The type of winter dormancy that some mammals and birds do is called hibernation. However, this is not merely a matter of going into a den and going to sleep, but requires complex changes beforehand. Hibernating animals readjust body temperature, metablolism, and heart rate. There is also an increase in magnesium in the blood and reduction in endocrine glands. While bears may be the best know hibernators, their body temperature only drops from approximatley 100 degrees to 93 degrees. They also give birth in the winter and for these reasons they are considered shallow hibernators. They are able to conserve energy, but their bodies do not undergo the level of physiological changes as some other animals, such as ground squirrels and bats.
While snow may seem like the opposite of warmth, it is actually able to serve as a good insulator and several animals make use of this. Snow actually traps heat close to the ground so this layer or subnivean zone may be only slightly below freezing, while the air temperature could be much colder. Voles tunnel through the snow as a way to both stay warm and avoid predators. In addition, grouse, ptarmigan, porcupines, wolverines, and bears also make dens in the snow.
Snow blankets the ground, ice crystals coat the trees, and a cold wind blows through the forest. While winter is a challenge for all wildlife, a large number have found ways to stay warm and even turn environmental conditions to their advantage. It is the ability to meet these challenges that can serve as a reminder of the amazing world we live in.