Waking From Hibernation, the Hard Work of Spring Begins

Fertilization happens a few days after females emerge from hibernation. After leaving their winter caves, they move to a large tree or another cave. “They want a warm, stable environment where they can develop their young,” said Joy M. O’Keefe, a bat expert and assistant professor at Indiana State University.

Bats often return to the same maternity spot year after year, sometimes traveling hundreds of miles to get there. Dozens of mothers will congregate at these sites, cuddling to keep warm. When their pups are born, 50 to 60 days later, mothers may help each other by taking turns foraging for insects and roosting with the group.

With no parenting responsibilities, and perhaps to avoid competing with the females, males will stay in torpor for longer — making their hibernation spaces real man caves in the spring.

Squirrels in an extended adolescence


An Arctic ground squirrel in Alaska’s Denali National Park.

Wolfgang Kaehler/LightRocket, via Getty Images

Arctic ground squirrels hibernate farther north than any other animal. They enter torpor in August or September, and stay in suspended animation underground for up to 270 days, reducing their metabolism by well over 90 percent to survive.

To achieve this, males shrink their testes and stop testosterone production, which means they must experience puberty every spring. When they awaken in mid-March, they live off a cache of seeds, berries, mushrooms and willow leaves while sexually maturing and bulking up.

When they surface in mid-April, the world outside is still covered in snow and temperatures can be as low as minus 20 degrees Fahrenheit. But the males are charged up. For two weeks, testosterone will surge through their…

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