Hibernation, also known as “winter sleep,” is when an animal’s heart rate and body metabolism go down drastically for days or months at a time in order to survive the chilly winter months.
Two types of hibernation exist. True hibernation is when an animal falls into such a deep state it appears to be dead. Whereas, torpor is a state when an animal’s heart rate and temperature reduce, but they are able to move around when needed.
Many animals hibernate during winter, but there are some you may not expect.
Many different species of rodents belong to the marmot family, such as groundhogs, chipmunks, ground squirrels and alpine marmots. They can hibernate for up to eight months straight, while maintaining a body temperature of 38 degrees Fahrenheit (3 degrees Celsius). During hibernation, they may take only 2-3 breaths per minute and their heartbeat falls to 3-4 beats per minute.
Not all birds migrate for the winter. Some populations of the common poorwill, native to western North America, hibernate during colder months. This is the only bird known to hibernate. It can settle underneath shallow rocks or rotten logs and stay there for up to five months. Its daily energy needs drop by 93 percent, and once hibernation is over, it takes seven hours for its body temperature to get back up to normal.
It’s ironic that bears may be the most famous hibernator, but they actually don’t truly hibernate. Bears go into a state of torpor during winter, where they can wake up and move around periodically. This allows bears to have their cubs during hibernation. Their heart rates and metabolism will also drop. In fact, they can last as long as 100 days without food or water.
Unlike mammals, hibernation in reptiles is known as brumation. Reptiles are cold-blooded, and therefore need to find warm hideaways to hibernate, such as holes in the ground or rock crevices. Certain species, like garter snakes, hibernate in groups to preserve heat. These are known as hibernacles, which can hold hundreds of snakes at a time. The largest snake hibernacles in the world are the Narcisse Snake Dens of Manitoba, Canada, where tens of thousands of snakes gather to overwinter together.
After rodents, bats are the second largest order of mammals. The 1,240 species of bats represent about 20 percent of all mammal species identified worldwide. They can also be some of the longest hibernators. Big brown bats often spend up to 66 days hibernating in the wild, although one bat kept in captivity hibernated for an amazing 344 days.
Despite the fact they live in tropical climates, some species of lemur hibernate. The fat-tailed dwarf lemur, native to Madagascar, hibernates for up to eight months. Winter temperatures may rise over 86 degrees Fahrenheit (30 degrees Celsius), but this is cold enough for the lemurs to seek refuge in tree holes until spring rains and more food are available again. During hibernation, they live off the fat in their tail and can lose almost 50 percent of their body weight.
Photo Credit: Wikimedia Commons/Frank Vassen
Different types of turtles have different hibernation strategies. Water turtles will bury themselves in mud and leaves at the bottom of a pond. Their body temperatures drop and they stop breathing through their lungs. They actually have specialized skin cells near their tail opening that provides enough oxygen from the water to survive. Land turtles will dig a burrow deep into the ground to ensure their safety from predators and freezing temperatures over winter.
Insects’ way of hibernating is to go into a state called diapause, which is a long-term suspension of life functions. For instance, the praying mantis will overwinter as eggs and emerge in spring. If an insect overwinters as an adult, many species will produce an antifreeze-like substance in their blood that protects them from freezing temperatures. Moths, ladybird beetles and bumblebees all hibernate as adults.
Snails can live up to 7 years in the wild. Although, in captivity they’re shown to live up to 25 years. Their relatively long life span means they need to hibernate over winter. They cover themselves with a thin layer of mucus to stay hydrated. Then they bury themselves and close the entrance to their shells with mucus. The mucus hardens to prevent predators from getting in during hibernation.
Frogs and Toads
In colder climates, frogs often hibernate along creeks and in small crevices of logs and rocks. They can store glucose in their bodies, which provides a food source and prevents them from freezing solid during winter. Land-dwelling toads may also hibernate. Some toad species are known to hibernate up to three or four years straight.