Cold weather, scarce food lead to torpor

By Sara Scudier

OSU Extension certified volunteer naturalist

Have you ever thought it would be easier to just hibernate though winter? Many animals have evolved the ability to become inactive when the temperature is less than ideal and food becomes scarce.

In temperate climates, food supplies are often seasonal. If your food source is available only part of the year, you will need a way to survive when that food source is no longer available. This leads some animals to migrate, some to gather and store food, and some to go into a state of suspended animation. This is called torpor, in which metabolism, heart rate and breathing slow down. The degree to which an animal reduces these bodily functions determines how deeply asleep they are.

Animals may be inactive for the entire season, such as groundhogs, or only when conditions are inhospitable, such as chipmunks. Those animals that hibernate for the entire season solve the problem of getting enough nutrition to get them through until spring by eating as much as possible when supplies are plentiful and storing the surplus as fat. Many of the mammals that hibernate are able to reduce their metabolism to a very slow rate. This allows them to survive the winter by gradually using up the fat reserves they built up during the summer when food was plentiful. Bats go into a true hibernation, meaning they are in such a deep sleep they may appear to be dead. During hibernation, a bat’s heart rate drops from 400 to 25 beats per minute, and its breathing slows so much that it might not take a breath for up to an hour.

Bears are light hibernators and easily awakened, so tread lightly near that bear’s den. Bears go into torpor during the winter months only if they live in cold areas. During that time, they don’t eat or drink for about six months on average, and they rarely urinate or defecate. In addition, female bears give birth to and nurse their young during torpor.

Hamsters will enter torpor for a few days to a week at one time when the weather is cold, but only if there is plenty of food nearby so they can snack during brief waking bouts. Pet owners have been dismayed when they found their hamsters dead, only to learn they were actually hibernating. Hamsters hate being wakened from this state, and the sudden disturbance can cause a heart attack, literally scaring them to death.

To learn about some of the mammals in our part of the country, go to: http://go.osu.edu/hibernate