As the days grow colder, we don our winter coats, find lost mufflers and mittens, and trek outside to retrieve another log for the fire. As the sleet and snow start to swirl, hot chocolate with marshmallows sounds pretty good. Temperatures falling low and fast? Inclement weather on its way? Time to stock up on favorite snacks, grab that extra blanket, and line up the DVD's for a long and chilly ordeal. If we're lucky, we'll survive to see another warm day.
But what about the creatures in the meadows, woods and forests, the fields, the shorelines, ponds, streams, and lakes, our own backyards? What do they do when ice and snow blanket the landscape and winter's chill holds the outdoors in a vise-like grip?
The answer? Animals adapt – sometimes in incredible and marvelous ways.
Adaptations make it easier for animals to survive. These depend upon certain structures of organisms, but the striking thing is what the organism does with the structures. This is known as behavior. Winter survival often depends on adaptations that feature some form of animal behavior.
Animals survive the cold blasts of winter because they are sheltered in some way. They might be in water or mud beneath the ice, in burrows or tunnels down in the soil, or in dens or nests in thickets and trees. Some of them are able to become largely inactive during cold periods. The less you do, the less energy you need – this is the key to making it. Activity requires energy, energy comes from food, and food can be scarce in winter. Water is also required, and it's hard to use when it's locked up in ice and snow. Inactivity means these animals can "wait it out", resuming normal business when the weather becomes favorable again.
Winter's chill seems to inactivate most "cold-blooded" animals, such as reptiles (turtles, snakes, lizards) and amphibians (frogs, toads, salamanders). They don't move about when it's cold because their body temperatures are tied to that of the environment. Most stay covered and dormant during cold periods. In extreme cold, they may undergo a mysterious phenomenon known as hibernation. This cyclic behavioral response to extremely cold temperatures and limited food supplies is a period of dormancy which is a natural part of the life cycle of many animals. Heartbeats and breathing rates fall dramatically, and body temperature takes a steep plunge. The hibernating animal undergoing these physical changes uses very little energy. Life goes on, but in a very reduced fashion. The creature relies on fat stores in its body that can usually meet the slight demand for energy. In extreme cold, amphibians will often hibernate in mud at the bottom of a pond or under a log where the mud and water do not actually freeze. Reptiles seek out remote and undisturbed resting areas, sometimes congregating in groups of the same or similar species.
A few mammals hibernate, entering into a state of torpor (dormancy) when the surrounding temperatures drop below freezing. In autumn they put on weight in preparation for the move to their winter dens – their metabolism slows so that the energy required for warmth is lowered. There are few mammal species that are considered "true hibernators", and these include woodchucks, some small rodents, some ground squirrels, and bats. Scientists believe that some creatures (raccoons, skunks, tree squirrels, bears) merely reduce their activity and go into a lighter "winter sleep", emerging now and then to forage and move about on milder days.
Some small mammals (mice, voles) neither hibernate nor winter sleep, using the snow as a protective blanket under which they go about their winter business. They live in tunnels and burrows and serve as food sources for predators (coyotes, foxes, skunks) that remain active and must hunt for food. Migration (birds) is another fascinating solution for some.
Whatever the method, animals in winter have a tough row to hoe. Many don't survive. The sighting of new and renewed life when the weather warms is testament to the triumph of nature's way. This spring, we look forward to seeing evidence of her success!