Let Sleeping Bears Lie

As December and the winter solstice creeps closer, the short days and dropping temperatures can leave us wanting nothing more than a cozy blanket and a crackling fire. The changing season also triggers hormonal and behavioral changes in the animals who call New York home. The animals who stay here year-round are amazingly well adapted to survive the harsh winters and shortage of food. For many mammals, this involves lots and lots of sleep.

A yearling black bear in its den.

A yearling black bear in its den.

The black bear has impressive strategies to avoid the problems facing animals who sleep for months at a time. To avoid starving, they spend most of the fall in a hormonal-induced feeding frenzy. By the time their appetites decrease, and they begin searching for a cozy den site, they will have a layer of fat, up to five inches thick, insulating their bodies and internal organs. This fat also acts as a built-in food source through the winter. Black bears will grow a longer and thicker coat to trap the warmth produced by their bodies against their skin. One of the more impressive black bear feats is managing to go the entire winter without excreting waste or moving; if a human tried such a thing, they would go into kidney failure, and lose extreme levels of muscle mass and bone density. Black bears avoid toxic levels of waste in their bodies by biochemically converting their waste products into muscle. They may even wake up in the spring with more muscle than they started with in the fall.

The sleep that black bears enjoy in winter is technically not hibernation, as their body temperatures "only" drop 10 degrees, it is called torpor. In New York, the "true hibernators" include groundhogs, jumping mice, and cave-dwelling bats. To belong to this elite group, an animal must meet some impressive criteria: their heart rates, breaths per minute, metabolisms, and body temperatures drop drastically and they basically go into a comatose state for the winter.

A groundhog, also known as a woodchuck.

A groundhog, also known as a woodchuck.

Take the groundhog, for example: their heart rate slows down to five beats per minute, they breathe just twice per minute, and their body temperature drops from 99 degrees to 37 degrees Fahrenheit; humans, on the other hand, can enter a state of hypothermia from a body temperature drop of just three degrees. If you come across a groundhog in its burrow, no amount of poking or ringing alarm clocks will wake it. If you stumble upon a black bear in torpor, however, beware: they may be groggy, but they can wake quickly if disturbed.

Although winter is a tempting time to sleep the day away, be sure to take advantage of the fact that we do not hibernate and enjoy the outdoors in all its crisp and snowy splendor. As you do so, think about the critters who might be sleeping underground nearby and stop to appreciate the ways in which animals have learned to make it through the season. And if you happen to come across a sleeping bear while you're out there, make sure to give him his space!


- Siobhan Prout, Outreach Educator