Imagine eating as much food as you could, then taking a nap. When you awoke, you’d realize weeks had gone by! What to do? Eat as much as you can and fall back to sleep! Repeat until it’s nice and warm outside. This is what many hibernating animals do, and they do it in order to conserve energy. (Many hibernating animals are small, so they lose body heat much more quickly than larger animals… I could explain, but it involves exponents…)

Bears aren’t typically considered small animals, yet the hibernate. Or do they? This seems to be an everlasting debate, but the current consensus (if there even is one) is that bears do hibernate–just differently from other hibernators. Black bears can maintain their body heat in winter if they choose, but they have a hard time finding enough food to stay alive in most places where they live. Hibernation is their solution to the food shortage. By hibernating, they can make it through the winter with just their fat.

When bears hibernate, their body temperature cools just a bit and their respiration and heart rate slow a little. They don’t eat or drink at all during hibernation (they even develop a fecal plug!) Since bears don’t cache food (like most other hibernators), they eat as much as possible before hibernation–a state called hyperphagia (literally, in Greek: over-eating). During hyperphagia, bears may eat 10,000 to 20,000 calories per day (compared to around 4,000 per day at other times).

So far this year, it seems like all the bears in Yosemite Valley are hibernating. There has been only one sighting this winter. This isn’t always true, and it’s not uncommon for a bear to be active the whole winter if enough food is available. Last winter, several bears remained active–perhaps because there was a bumper crop of live oak acorns that persisted even until spring.

I wonder sometimes… what would it be like to be able to hibernate?