In November, we notice the number of wild animals has greatly dwindled. Winter strategies for Minnesota’s native species include migration, coping and hibernation. Purple martins fly to Brazil for the winter after their summer nesting season. And gray squirrels remain active in their home landscape year-round while thirteen-lined ground squirrels (a k a Minnesota gophers) escape winter by hibernating underground.
A gopher plugs the burrow opening before beginning its long sleep, then curls into a ball, nose touching its belly and tail over its head. The heartbeat drops from 200 beats per minute to about 17. It consumes about 7 percent of the oxygen used while active. The body temperature sinks to 37 degrees. Severe cold with freezing temperatures penetrating deep into the soil can awaken gophers from their dormancy. This causes their body temperature to rise and prevents freezing to death.
Hibernation is a winterless life chosen by reptiles, amphibians, insects and some mammals. During the winter untold millions of animals — including toads, frogs, salamanders, snapping turtles, garter snakes, bats, woodchucks and mosquito larvae — are hibernating across Minnesota.
The physiology of this “sleep” is amazing. The animal’s breathing nearly stops. The blood thickens. The internal temperature drops. Metabolism slows. The kidneys and digestive system practically stop functioning. Hibernating animals can “sleep” through most disturbances. A few are able to wake up if their body temperatures approach freezing, but this seldom happens as many animals hibernate below the frost line on land or below the ice under water.
Jim Gilbert’s Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays. His observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.