Distinctly Montana Magazine

d i s t i n c t ly m o n ta n a • w i n t e r 2 0 1 5 22 W ith temperatures that often dip well below zero, and food that is sometimes hard to come by, winter poses unique challenges to wildlife, especially those living in Montana. One survival strategy is to migrate south like many birds. Another strategy is to hibernate like ground squirrels. Some, like the little brown bat, do both. But what exactly do we mean by migration and hibernation? Think of migration as an annual round-trip ticket with regular, seasonal move- ments between a summer range and a wintering area. A young fox that leaves its natal den in search of its own territory is not migratory, nor is the cottontail living in your garden that occasionally visits your neighbor's yard. But a flock of sandhill cranes that flies south to New Mexico for the winter and returns the following spring is migratory, as is a bighorn sheep herd that moves from its alpine summering range to a winter grazing area in the foothills every year. Many people believe that animals migrate to escape the cold, but this isn't true. Animals migrate to follow seasonal changes in the availability of food. While some animals migrate, others, like the ground squirrel, prefer to hiber- nate. Like migration, hibernation occurs when food is in short supply. Ground squirrels have one of the longest hibernations of any animal — often disap- pearing into their subterranean burrows for seven or eight months a year. The classic definition of hibernation is a period of deep sleep where an animal's body temperature dips to just above freezing for weeks at a time. In addition, a ground squirrel's heart rate and breathing slows dramatically. A low body temperature, heart rate, and breathing rate all help the ground squirrel conserve energy. Ground squirrels and other hibernators also put on a thick layer of fat that will fuel them until spring. Now that we know what migration and hibernation are see if you can answer these questions about how Montana's wildlife cope with winter. 1. grIzzly BEarS SoMEtIMES waKE uP durIng MIgratIon and lEavE thEIr dEnS. doES thIS MEan that BEarS arEn't truE hIBErnatorS? No. Both grizzly and black bears are true hibernators. It was once thought that bears weren't true hibernators because they didn't fit the classic definition — a reduction in body temperature hovering around freezing. Bears reduce their body temperature by only about 12 degrees which means they are easily aroused while hibernating. But, unlike other hibernators bears don't need to awaken during their winter slumber. Because ground squirrels and other animals hibernate at such low temperatures they need to increase their body temperature for a day or two every few weeks, otherwise they wouldn't survive. Because a bear's body temperature remains well above freezing they don't have to wake up. And, unlike ground squirrels and other hibernators, bears don't defecate or urinate during hibernation. Instead they recycle urea into proteins for maintaining muscles. Bears are now considered to be highly efficient hibernators. 2. ground SquIrrElS and SoME BatS hIBErnatE, But whICh of thESE SMall MaMMalS alSo SPEndS thE wIntEr hIBErnatIng? a. Yellow-bellied marmot B. Pika C. Badger d. Raccoon If you answered a, you're right. Both the yellow-bellied and the hoary marmot, along with other ground squirrels and chipmunks hibernate. (Tree squirrels remain active all year). Although pika, badgers, and rac- coons spend much of the winter in underground burrows they don't hibernate. Instead they go into periods of rest called torpor. Torpor is sort of a mini-hibernation that helps reduce the food they need during winter. fox Hibernation ...Migration? by LISa barIL aMerican robin prongHorn pika

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