August 30, 2008
By Susan Benson,
CNHM Director of Education
Have you noticed mallards and other ducks migrating? Or have you run into a chipmunk scurrying across the ground, cheeks bulging twice the width of its head with hazel nuts? Or your pet cat, dog, or rabbit beginning to grow a thicker coat as the days grow shorter?
It is only early September, but winter is coming, and animals have strategies for coping. Breeding has been timed so that offspring can grow and develop enough to survive their first winter. These young have time now to grow their first winter coat. Mothers who have lost weight when nursing now have time to improve their condition before winter.
Some animals leave the area through migration. Land animals have a more difficult time with migration because walking is much less efficient than flying. For those animals that stay, there are other options. Body size determines where the animals that stay end up spending the winter. A moose, for example, with its long legs, can walk through the deep snow, but smaller animals cannot, so they have to prepare to spend winter either under the snow or in areas with little or no snow. The big brown bat will soon begin searching for a winter habitat—that may be in an outbuilding or your attic. Keep a lookout for any of the signs of animal preparation for the coming cold season.
The trigger for the change in animal physiology and behavior is the photoperiod—the relative length of light and darkness during a given day. With the relative increase in darkness, many big mammals gain fat between their internal organs and under the skin. In preparation for their long winter sleep, or hibernation, woodchucks grow enormously fat toward the end of the summer. During autumn, black bears eat more than usual to gain body fat to sustain them through their winter “slumber.” Bears do not truly hibernate, but rather fall into a deep sleep from which they can awaken quickly. During late summer, a bear will eat five pounds of food per day in preparation for winter. Imagine eating five pounds of acorns! Northern small mammals gather so-called brown fat, which generates heat very effectively. Black bears and other hibernating animals maintain this same brown fat because it has the ability to dissipate stored energy as heat.
The fur of foxes, badgers and squirrels thickens to allow them to keep their body temperature constant during the cold weather. The snowshoe hare begins growing its white fur coat, beginning with its ears and tail; the total color conversion takes about 10 weeks. The short-tailed weasel also changes its fur coat to white with the exception of the black-tipped tail, which is thought to be an adaptation so that when the weasel is being chased, the pursuer will focus on black tail tip and miss catching the weasel.
White-tailed deer are affected as well; in late summer, a gland in their brains stimulates the reproductive organs. In bucks, hormones increase and the antlers harden and the velvet is shed. The period of hard antler lasts from early September to early February. We are familiar with bucks rubbing against saplings and smaller trees, removing the outer bark, and exposing the tree’s cambium underneath. The bucks then rub the cambium with their foreheads, where a scent gland is located, leaving a sign of their presence left behind for others to discover.
Some mammals, like squirrels, mice, and beavers, gather extra food in the fall and store it to eat later. Squirrels store their food, either in centralized heaps, or buried in the ground, sometimes with just one nut or acorn in each hole. Squirrels will cover their hiding place with care; these caches are usually found within 75 feet of where the squirrel found the nut or seed. When the snow cover thickens, the squirrel digs out the hiding places, and after having eaten some of the seeds, hides them again, this time closer to the snow surface. Some squirrels even store fungi in the branches of the trees. In a good fungus year, one might see dried and darkened mushrooms hanging on the lower branches of trees. During the late summer and fall, beavers also put food away, storing branches at the bottom of their ponds in preparation for winter.
Become a phenologist! Create your own backyard winter habitat by constructing a pile of logs, rocks or leaves—ideal winter lodging for mice, shrews, rabbits, toads, frogs or other small animals. Enjoy watching the outdoor action as our mammal neighbors harvest nature’s fall treats.
Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 43570 Kavanaugh Street or on the web at www.cablemuseum.org to learn more about exhibits and programs.