Hibernation

By Bob Dispenza, Park and Education Manager, Allen County Parks

With cold weather approaching, those of us who don’t like skiing, sledding or skating may wish we could hibernate through the winter. While leading hikes, I usually discover that hibernation is widely misunderstood. But just what is hibernation, and who does it here in Indiana?

True hibernation is not like sleeping. It’s much closer to being dead. If you are sleeping and I shake you or make a loud noise, you may awaken. If I were to take a hibernating woodchuck out of his burrow, I could bounce him on the floor like a basketball and still not wake him. Hibernation involves a change in metabolism – how fast an animal burns energy. The point is to conserve energy for a long period of fasting in winter. An animal’s waking temperature may be 100°F, heart rate may be 100 beats per minute and breathing 70 times per minute. While hibernating, the same animal’s temperature may drop to 40°F, heart rate to 10 beats per minute, and breathing to 3 times per minute or less. Animals whose temperature does not drop (bears) are not true hibernators.

Cold-blooded animals (snakes, frogs, lizards, fish, insects, etc.) have no choice but to become inactive or die when temperatures drop below about 45°F, though gray tree frogs can freeze solid and still revive in the spring.

Though colder temperatures and the amount of fat an animal has put on help determine when to hibernate, the main cue is photoperiod. Shortening days in fall cause changes in behavior that lead to hibernation. Rising temperatures in spring appear to be the main reawakener.

Torpor is the temporary lowering of metabolism. A few warm-blooded animals use this as a short-term measure to overcome short-term adversity. Hummingbirds, who could starve to death overnight, may become torpid at night. Some carnivores and small mammals will do this also, especially during severe winter weather.

There are only a few warm-blooded species native to Indiana that actually hibernate. They can survive on stored fat without eating or drinking for several months. Probably the most famous is the woodchuck (Marmota monax), who uses up 30% of his fall body weight during hibernation. You could watch for him on February 2 (we’ll be having a special program that day at Metea County Park), but don’t expect to see him. All our native bats hibernate, though some fly south to do it. Bats also use daily torpor to conserve energy during adverse weather that keeps their insect prey from flying. Thirteen-lined ground squirrels (Spermophilus tridecimlineatus) are not common in Allen County, but are true hibernators. Their 200 beat-per-minute heart rate drops to below 20 beats per minute. Two species of jumping mouse – woodland (Neozapus insignis) and meadow (Zapus hudsonius) – look a little like miniature kangaroos. Up to 75% of hibernating meadow jumping mice never reawaken in the spring, having used up their fat reserves before warmer weather arrives. This completes our list of hibernators. All the other warm-blooded animals must struggle through winter, eating stored food or foraging as best they can. Even if they don’t make it, they will provide winter food for some other animal.

So if you’re considering hibernating this winter, don’t be like the jumping mice – put on plenty of extra weight. Pile on the gravy and stuffing, and go ahead, have that extra dessert.