How many of us are still digesting our Thanksgiving meal(s) and continue to clean out our refrigerators, eating the leftovers? This time of year we tend to eat, and eat, and eat some more. Data tells us that the average American will gain between 1 - 5 pounds between Thanksgiving and the New Year. That is not a lot for one year, but over time, if those pounds are not lost, they can add up, so be aware. This ‘natural weight gain’ is a great excuse to get outside for a brisk walk or family hike. In nature, during winter, where there are not fireplaces and an abundance of food, how does the cold impact eating and survival?
Many animals that live in cold environments, where food is scarce, have something called “hibernation inducement trigger”, or HIT, in their blood during their hibernation season. Research has discovered that when this substance is injected into animals during the spring, hibernation behaviors can be induced. Interestingly, the exact chemical identity of HIT remains elusive, but it appears to be similar to an opiate, which may help to explain how it decreases heart rate, breathing rate, and general metabolic (energy) demands. This helps animals conserve energy, which helps them to survive the winter with little or no food.
To prepare for such an event as hibernation, animals undergo a feeding frenzy called “hyperphagia” where the animals will eat a lot of calories to build up energy reserves in the form of fat. For example, a black bear in Alaska will feed at a frenzied rate from midsummer thru the end of autumn, consuming 20,000 or more calories in a day. We did the math, that is like eating 31 McDonalds Big Macs a day! This allows the bear to add 4 - 5 inches of body fat, which nearly doubles the insulation capacity of their pelt.
The metabolic slowdown is significant. Heart rates plummet. For example, a hibernating woodchuck’s heart rate will decrease from 80 beats per minute, to as slow as 4 beats per minute. This causes the ‘true hibernators’ to appear dead. True hibernators include the jumping mouse, the little brown bat, the eastern chipmunk, and some ground squirrels. There is even a bird that hibernates. The Poorwill, which is Hopi for, “the sleeping one”, is a nocturnal (night) bird found throughout the southwest which enters into this slower state for days or weeks at a time.
Hibernation is not the only way animals survive the harsh environmental conditions of winter. Animals also migrate, moving themselves to a place where food can be found. This is a common tactic for birds, bats, caribou, elk, and whales. Fish also tend to migrate in their own right, heading into deeper water. Insects, like butterflies and moths, also migrate. Like fish, earthworms also seek deeper depths to avoid the frigid surface temperatures.
Adaptation is another way animals survive winter. Much like us putting on an extra layer of clothes, one way animals adapt to the cold is by increasing their fur capacity. Another winter adaptation is changing their eating habits during winter. For example, rabbits and deer may eat bark, moss and twigs instead of the grass that is available in the spring and summer.
Preparation and survival for winter by non-human animals is a fascinating topic that science continues to investigate. It is nothing short of miraculous how the animals know what to do for survival, and when to do it. As a human, however, during these cold months when the couch is calling and pie is readily available, we do not need to store up our energy reserves, so get outside, it is good for humans everywhere.