Did you know that the Siberian salamander (Salamandrella keyserlingii) can survive for more than a decade, frozen in solid ice, feet below the surface of the earth? When they are thawed, they will walk away and start catching bugs!
They, and many other animals, including some fish and amphibians, manage to not freeze to death because they develop ‘antifreeze’ chemicals that replace the water in their blood and their cells. This is just one of the many adaptations that animals have developed to survive cold winter weather.
When the temperatures dip well below freezing up here in the high elevations of the Sierra Nevada, we modern humans (Homo sapiens sapiens) have access to all sorts of luxuries to help us stay warm, dry and fed. But our other community members, the plants and animals with which we share our home, have been living up here for millennia without the technologies that we utilize to survive winter in the Sierra.
The biggest problem facing animals during the winter is actually not the cold, but the shortage of food. The most difficult time for winter animals is when extreme cold is combined with an insufficient snowpack, like we just experienced in mid-December. This combination prevents many animals that rely on the snowpack for insulation while actively foraging for food. If they do forage without this insulation, it leads to an enormous loss of energy.
Many animals avoid this problem simply by getting the heck out of Dodge. Or Truckee, as it may be. Birds, insects, and mammals of all shapes and sizes head to warmer climes where they have access to a reliable food source, returning to our region when the days are longer and the food more plentiful. Some birds go all the way to the Southern Hemisphere in search of eternal summer, but many birds and other animals simply head to lower elevations in the winter.
While some animals leave our region, many stay up here and brave the cold and dwindling food supplies. Some animals that stay behind hibernate through the winter. Hibernation is different from sleep because with normal sleep, animals move a little, have active brains, and can wake up very quickly. During hibernation, animals’ heart rates, breathing rates, and body temperatures all drop to very low levels.
For example, when the Golden-mantled Ground Squirrel (Spermophilus lateralis) – that baseball-sized rodent that looks like a chipmunk, but without the eye-stripes – goes into hibernation, its heart rate will drop to as low as two beats per minute, it will only breath about once every 30 seconds, and its body temperature may drop to 6-degrees Celsius.
Other true hibernators include bats that will hibernate in caves in big groups to stay warm, frogs that will hibernate at the bottom of streams and ponds where the water does not freeze or under leaves and dirt below the snow, and snakes that will gather together by the hundreds under rocks, in burrows, or in basements. I’m sure Indiana Jones would not appreciate coming across one of those places.
Contrary to popular belief, the Black Bear (Ursus americanus) does not actually go into ‘true hibernation.’ Their heart rate and body temperature still remain relatively high compared to true hibernators. However, bears can remain in a deep sleep, or torpor, for six months, during which time they may not eat or drink. Bears will often get up and move around during this period, and will sometimes even come out for food and water. Females give birth and feed their newborns in their den during the winter.
In the late summer and fall, before going into hibernation or torpor, animals eat a lot of food so that their bodies are able to live off the stored body fat. But a lot of animals survive the winter by staying active the whole time. They grow a layer of fat and warmer fur or feathers and then eat all winter to keep the fat built up.
The Snowshoe Hare (Lepus americanus) and one of its predators, the Long-tailed Weasel (Mustela frenata) both adapt to their winter habitat by growing a white coat in the winter in order to blend in with the snow. The Snowshoe Hare and another of its predators, the Bobcat (Lynx rufus), both grow dense fur on the bottom of their feet so that they can move quickly across the top of snow.
Other mammals that are active all winter are shrews, mink, beavers, voles, foxes, and tree-dwelling squirrels. Beavers and squirrels have large food caches built up so that they can eat all winter. Deer and rabbits search for food under the snow. Shrews, mink, weasels, and fox hunt animals all winter.
While many of the birds we observe up here in the summer migrate away in the winter, some birds can stay in the cold Sierra, including grouse, chickadees, woodpeckers, hawks, and owls. To stay warm, they grow warm winter feathers. Blue Grouse (Dendragapus obscurus) burrow into a snowdrift during cold spells and use the snow to protect them from the freezing air.
So remember that those of us humans who stay up here all winter do so in the good company of hearty, well-adapted animals.
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