Good Question: How Do Animals Know When To Come Out Of Hibernation?

MINNEAPOLIS (WCCO) -- We will soon begin to see some of Minnesota's most-beloved creatures come out of hibernation.

Different species of bats, bears, turtles and snakes all hibernate here, and many rely on more than warm weather to wake up.

So how do animals know when it's time to come out of hibernation?

Garter snakes hibernate in the hundreds, and in some cases thousands. And when they wake up, it is like a squirmy ball of green spaghetti.

"It's temperature dependent, so they usually get underground before the ground freezes solid," said Lori Naumann, a non-game wildlife information officer with the Minnesota Department of Natural Resources.

She said like many animals, snakes stock up on food and then get underground before the ground freezes.

They rely on fat deposits to get through the winter, and heat to wake them up in the spring. Many species of frogs and turtles do the same.

"Some animals it is temperature dependent and it's weather and daylight dependent, which is the case for snakes," Naumann said. "But other animals, it's hormonal."

We have the convenience of an alarm clock, but ground squirrels rely on their brain. Naumann says they rely on the thalamus to tell them it is time to wake up.

Metabolism, breathing and heart rates decrease in almost all cases of hibernating animals. It can even drop to two beats per minute for some.

"If you pulled them, like for instance ground squirrels, out of the very frozen ground, they would not wake up at all," Naumann said.

But for many hibernating animals in Minnesota, like black bears, it is not a true hibernation. They have their young in the den, so they are still on guard.

"They can wake up and be startled, and they can wake up and protect their young," Naumann said.

But they will stay in their den in that state for six months or more. When food sources return, like berries, so do the black bears.

Naumann says hibernation and migration go hand in hand.

Instead of hibernating when food runs out, many birds migrate south in search of other food supplies.

Animals like deer, and birds like robins, can find food year-round, so they stay awake during the winter months.