​Animals use three strategies to survive winter’s chill: migration, hibernation or toleration of the cold.
By Tom Koritansky, Natural Resource Manager
When the cold and snowy days of winter come upon us in northeast Ohio, many of us are prepared to deal with the frigid temperatures, lake-effect squalls, short days and long nights. It’s easy for us to don a few extra layers or turn up the thermostat a few degrees to stay warm. Animals on the other hand don’t have that luxury, but they do have ways to survive some of winter’s harshest conditions.
Generally, animals use three strategies to survive winter’s chill: they either migrate, hibernate, or simply tolerate the cold.
Migration involves the movement of a group of animals from one location to another. Animals that migrate may only move a short distance or across a vast expanse. For some, their migration may take only a few hours while others may take weeks to reach their destination. Migration takes a lot of energy and it’s a stressful time for an animal. In order to successfully migrate, animals must build up their stamina in order to survive the journey; this often involves increasing their energy intake to build up their fat reserves while traveling.
Opossums sleep during the coldest parts of winter but awaken to look for food.
When we think of animals that migrate, we often think of the many species of birds that fly south for the winter. For many birds, the end of summer signals that it’s time to start preparing for the journey south. Shorebirds begin to move in the late summer and swallows (including the barn swallow) start to stage and soon take off for warmer weather. Also, by this time warblers (like the yellow warbler) pass through the area in good amounts. As fall approaches, the number and variety of birds preparing to migrate increases. Throughout the month of September, a wide variety of songbirds pass through our area, including but certainly not limited to thrushes, vireos, and flycatchers. By the time October arrives, the warbler migration has crested, only to be surmounted by shorter-distance migrants like ruby-crowned and golden-crowned kinglets and winter wrens. Waterfowl migration ramps up during the month of November with many ducks and geese reaching their peaks. By December, most species have peaked, but a few stragglers might be found.
While migration is a fitting strategy for birds who are adapted to traverse long distances in order to seek out ideal conditions, other animals can’t expend that much energy in order to survive so they use other strategies. For some other animals, hibernation is the approach they use to survive winter’s chill. Hibernation is the long-term dormancy or inactivity of an animal. Animals eat heartily during the fall to build their fat reserves for the upcoming dormancy. As animals enter a state of hibernation or torpidity their heart rates slow, body temperatures cool, and energy requirements drop. For animals that can seek shelter in a secure spot, it’s an effective strategy to conserve energy and survive winter’s chill when food and water might be scarce. Animals that hibernate do so along a continuum from true hibernators (animals whose body temperatures drop extremely and respire very slowly) to those that enter various states of torpor or controlled hypothermia. The body temperatures and heart rates of these animals also drop, but not nearly to the extent of true hibernators, so they are more easily awakened. The only true mammalian hibernators in Ohio are jumping mice, groundhogs and little brown bats. Skunks, raccoons and opossums are some examples of animals that sleep during the coldest parts of winter but awaken to look for food when there is a break in the weather.
The only true mammalian hibernators in Ohio are jumping mice, groundhogs and little brown bats.
Animals that don’t hibernate or migrate have developed adaptations and behaviors to help them simply resist and tolerate the cold. Winter birds in Ohio like dark-eyed juncos and white-throated sparrows mingle with year-round resident blue jays, cardinals and chickadees. With small external appendages such as ears and legs, radiating heat is kept to a minimum. Many birds have an antifreeze adaptation known as a counter current heat exchange system in which the arteries and the veins in the feet and legs run side by side, allowing cold returning blood in the veins to be warmed by the arteries. Feathers help conserve heat and keep exposed skin to a minimum. Some mammals, such as white-tailed deer and squirrels, remain active all winter. White-tailed deer browse on woody plants and can be found in sheltered forests. Squirrels get ready for winter by building caches of nuts and seeds in the fall. Fox squirrels might be seen hiding individual nuts, while red squirrels hide all of their food in one location.
Even though our natural areas may appear to be still and subdued during the winter, there are some complex systems working behind the scenes. There is still plenty to enjoy during a winter hike along a trail.