On a cold, snowy winter’s day, it’s easy to think of animals cozily curled up in a burrow or a cave, hibernating for the winter. True hibernation is a state of deep sleep, or torpor, where an animal’s respiration, temperature, and heart rate become drastically reduced. The idea is to conserve as much energy and body fat as possible until warm weather returns. Only three Maine mammals are true hibernators: woodchucks, jumping meadow mice, and bats.
- Skunks, chipmunks, porcupines and skunks wake on warmer days to forage.
- Smaller mammals like mice, burrow tunnels under snow.
- Beavers stay in their lodge with the food they’ve stored for the winter. Trappers know when beavers are home by placing their hands above the dams’ air vents. If the air is warm, there are occupants.
- A black bear’s heart rate drops from 40 to 10 beats per minute, and its oxygen intake is cut in half, but its body temperature drops only a few degrees. If a sleeping bear is disturbed, it can wake up fairly quickly. Maine’s wildlife biologists report, “When [we] go into their dens in the winter, mama bear is wide awake.”
What about other animals?
- Many species of frogs burrow under the frost line to wait for spring. Others sleep through the winter in ponds – you may actually see a frog swimming under the ice! Wood frogs can actually freeze solid for the winter; they have a chemical like anti-freeze in their blood that allows them to thaw in the spring.
- Snakes hibernate together in a community den.
- Many birds fly south for the winter, but we have some hardy species that brave Maine’s winter. The chickadee has an amazing adaptation of going hypothermic on nights where temperatures are extremely low. Chickadees lower their body temperature in a controlled manner, down to about 12 or 15 degrees below their normal daytime temperature of 108 degrees F. This remarkable adaptation allows the bird to conserve almost 25 percent of its hourly metabolic expenditure.
Just thinking about it makes me want to curl up by the fire!
– Erika Carlson Rhile, CELT Education Committee Chair