The many forms of wildlife hibernation
~wildlife education~
A bear’s winter den. Photo credit: istock.com/ Gennaro Leonardi
How do wild animals survive in winter when the weather turns cold and natural food sources are scarce?
Many animals hibernate or go into “winter sleep”. During hibernation, an animal’s heart rate and body temperature and movements slow down.
Unlike many small mammals, bears do not actually hibernate; instead, they go into torpor, which is a state of decreased physiological activity, usually marked by a reduced body temperature and metabolic rate. Bears may not eat, drink, urinate or defecate for up to six months during their winter sleep, relying entirely on fat reserves they have accumulated. This adaptation prevents starvation when food is unavailable.
During torpor, the animal can wake up quickly to avoid danger, defend its territory or if there is an opportunity to feed.
Most B.C. black and brown bears den for four to six months every year, entering the den in November or December, and emerging in March or April. However, Vancouver Island bears may sleep for a much shorter time as our climate tends to be more temperate. Dominant male bears often emerge first in early spring, while females with cubs may remain in dens longer, sometimes until late May.
Over-wintering hummingbirds like Anna’s Hummingbirds also practice torpor. If they haven’t consumed enough food to get through the day, their body temperature and heart rate will reduce dramatically. They can lower their metabolism by 85–95% and hang motionless on branches for hours.
Hibernation for reptiles and amphibians is called “Brumation” which is another form of becoming dormant. Ectothermic or “cold-blooded” animals such as fish, frogs, snakes and turtles will burrow themselves in the mud or under leaves and rocks in the winter. Insects find shelter in holes in the ground, under the bark of trees or inside rotting logs.
You can help wildlife in your garden by leaving leaves on the ground to provide coverage for small creatures. A heated bird bath can be a vital source of drinking water. Hummingbirds can remember which feeders freeze and which ones don’t, and which houses radiate heat. Your hummingbird feeders may be crucial for the birds’ survival. Attach a heater or bring the feeders indoors overnight on very cold nights, but do not increase the sugar content in the sugar water from the standard 4 parts water:1 part sugar ratio, as it could harm the birds.
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