We have heard the words “winter storm warning” a great deal this winter. NOAA says that means a storm that “could pose a threat to life and property” including white-outs, wind chills and frostbite. So, we dress warmly, heat our houses and shovel - and shovel and shovel.
The critters don’t have snowplows, wood stoves or parkas, so they adopt other strategies. One is to be larger than their cousins in warmer climates. Our large mammals, like moose and bear, and non-migratory birds, like ravens, are bigger because it is easier to keep warm that way. This is called Bergmann’s Rule. Animals lose heat based on their surface area, so it might seem that a larger surface area would lose more heat. However, larger volume slows the heat loss. Overall, larger animals are able to conserve more heat. There is another factor in this equation as well: There are fewer species of everything in the north, so these large animals have less competition for food and are able to eat more and get larger.
However, our smaller furbearers aren’t larger in the north. The same strategy doesn’t seem to work for them. Many of them live under the snow in the subnivean environment which protects them from the stormy stuff. The temperature is more stable there and the wind doesn’t blow. Some of them huddle together to conserve warmth.
Members of the weasel family, such as mink, marten, weasel, otter and wolverine, make a compromise. They dig elaborate tunnels and feeding dens in the ground or under the snow. But they are predators, so they spend time outside their dens hunting on land or in the water. They have feet that allow them to travel easily on snow.
So what about the little ones that don’t live under the snow? The golden-crowned kinglet is a little bird that lives in the trees year-round. It is four inches long with a wingspan of seven inches, and weighs two-tenths of an ounce, no bigger than a hummingbird but with more feathers. It maintains a higher body temperature than most birds, at about 111 degrees. It can fluff its feathers up to an inch thick, squatting to cover its feet and tucking its head. It is a voracious hunter, eating three times its weight in insects daily. It finds insects in the winter by hovering and hopping along twigs searching for tiny prey. It must forage constantly to stay alive. Often, it will huddle with other kinglets at night to stay warm.
Some animals, like toads and bark beetles, make a sort of antifreeze. The reason freezing kills animals is that ice crystals form in their cells and cut the cell walls. So, if you can keep the ice out of the cells, you can live through freezing temperatures. Bark beetles and toads do that by producing glycerol (a chemical relative of the antifreeze you put in your car) in their cells. The liquids between the cells can freeze as long as the cells don’t.
Meanwhile, inside the bear dens, bear cubs will soon be born. They are small – about fist-sized, hairless and blind at birth, weighing about a pound. The sow is in a state of dormancy, but the kids know what to do, and are quite noisy about it. They will nurse for about three months. When they come out of the den, they will be about fifteen pounds. How many cubs a sow has will depend on how much fat she was able to store the previous summer and fall. She will only give birth to the number of cubs she can “afford.” Any other fetuses will be reabsorbed to assure that mom will make it to take care of the new cubs.
If you have questions or observations, please call Pam Randles at the Takshanuk Watershed Council, 766-3542, or visit http://www.takshanuk.org and add your observations and photos.