The first frost of the fall occurred in the middle of October at my house which was not unusual. However, since then the weather HAS been very unusual…or maybe the new normal? Even though the days are getting longer since December 21, we should be gripped by much colder temperatures and several inches of snow. But I was raking my leaves for the last time on DEC 26!!!! Yes, the day after Christmas. Unlike most, I am not a big fan of these warmer temperatures, I like it cold! I want SNOW!!! (yes, I am stomping my feet)
Even with this unusually warm weather, this time of year always makes me wonder what animals do to survive the long winter. Most people think that many animals “hibernate”, but that is not entirely true. Animals have adapted a variety of strategies to deal with winter and the serious lack of food that exists during cold months. Many birds migrate. Some are flying south great distances to Argentina and Chile. While others fly south to Ohio. Birds that have spent the summer further north, including Robins, Juncos, and the American Tree Sparrow may migrate to northeast Ohio for a “warmer” winter stay. Occasionally we will get an “irruption” of birds from the north looking for food as is the case this year with the Common Redpolls, Red Breasted Nuthatch, and Evening Grossbeaks.
Most mammals remain active for much of the winter. Fox, deer, coyote, rabbit, squirrel, opossum and raccoon tracks can be seen in the snow as they hunt and gather food. Other animals enter some sort of dormancy state. Dormancy is triggered by photoperiod (shorter periods of daylight) and temperature. Rather than battle the cold and treacherous conditions of winter and lack of food, these animals shut down for a period of time, sometimes many months. There are several strategies that fall under the title of dormancy, including diapause, brumation and hibernation.
Diapause is most common in insects and other arthropods and refers to a period of inactivity triggered by environmental factors. Such factors can be cold temperatures but may also include drought conditions during the summer months. A few insects survive by entering diapause as adults or pupa during the cold months. There are three butterflies, the Question Mark, Comma, and the Morning Cloak, enter diapause as adults and overwinter under bark of dead trees. During warm days in late February you may see them flying around. Pupa of many beetles and moths can be found in diapause during the winter months. It is fun to roll over a log during winter and see some of the insects you can find that have entered diapause. However, many insects emerge in the spring from eggs, grow into adults, the adults lay eggs during the summer and fall and then die. The eggs survive the harsh conditions of winter and hatch in the springtime, starting the cycle again.
Hibernation is a term restricted for endotherms, or warm-blooded animals. These animals enter a deep sleep in which heart rate and body temperature decrease. There is much debate on what animal is a true hibernator. Research has proven that bats and groundhogs are the only true hibernators of northeast Ohio winters. Hibernation should not be confused with Torpor. Torpor is similar to hibernation, but for much shorter periods of time. Many birds such as the Black-capped chickadee may enter torpor daily to deal with cold nights to conserve energy. Hummingbirds enter torpor throughout the summer to conserve energy. During winter, the torpor period is extended dramatically for some mammals. Most people think bears hibernate, instead, they enter a state of torpor. Bears, mice and chipmunks’ heart rates decrease but body temperature stays near normal for weeks at a time.
What do other cold-blooded (ectotherms) animals do in the winter? The strategy for survival is like hibernation. Turtles, snakes, frogs and toads enter a state of dormancy called Brumation. This process also involves a decrease in body temperature and heart rate. Amphibians and some reptiles burrow in the mud until temperatures begin to warm. Snakes seek their “hibernaculum”, sometimes with many other snakes. Fish move to the lower depths and remain there until the water warms. Wood frogs and spring peepers can freeze solid during the winter. That is why they are one of the first animals you hear in the spring looking for a mate.
For a wonderful book to read during a cold winter day, provided we get one, about animals in winter, read Winter World: the ingenuity of animal survival by Bernd Heinrich or Winter an ecological handbook by James Halfpenny.
