How do animals live through our winters?

For the Gazette

Friday, December 15, 2017

A ruffed grouse in winter

Each year as autumn advances I find myself amazed anew by the ongoing cycle of life in the face of approaching sub-freezing temperatures. Water, the facilitator of life processes, freezes solid and life-giving processes cease. Dormancy, hibernation, migration — there are so many strategies by which life manages this potential catastrophe.

I imagine incremental changes, as our North American climate cooled over eons, allowing organisms to continue inhabiting these latitudes. What amazes me most is that many animals remain active here through the snowy months.

Ruffed grouse, for example, are active in our forests all winter and spend most of their time on the ground. They seldom fly more than a couple hundred yards. They don’t migrate, but spend their entire lives on a territory of a few acres.

At barely over a pound and a half they are not a large bird. In autumn they molt in a thicker coat of feathers, almost double the thickness of summer plumage. Winter body feathers have a well-developed “aftershaft,” a sizable downy offshoot of the main feather shaft. This creates, in effect, a double layer of feathers with which to trap air and provide good insulation.

Ruffed grouse find nutrition in the winter buds of quaking aspen and other trees. Although this diet is usually readily available, it is not very digestible, so grouse have to eat a lot of it. Consequently, their digestive tracts get bigger in winter to accommodate this greater volume of food. In addition, some grouse apparently have the capacity to fast for two or three days, if necessary, living on stored fat and the contents of their crops.

Ruffed grouse trek over the snow on snowshoes of their own making, growing small, fleshy, comb-like bristles, called pectinations, along the sides of their toes. These fringes increase the ratio of foot surface area to body weight and conserve energy in their walks through the snowy forest. They shed the pectinations in the spring.

Grouse also create temporary overnight shelters by flying full-speed into the depth of snow drifts, creating a mini-impact crater, and then snuggling deeper to spend the night under an insulating blanket of snow crystals and trapped air. This works wonderfully except in the rare occasions of overnight ice storms that freeze before the grouse emerge in the morning.

White-tailed deer also remain active in our forests. In winter they grow insulating fur. Heat crosses spaces of still air very slowly and the hairs in their coat trap air spaces among them. But deer go further than this. They grow coarse, thick, hollow, dark guard hairs (approximately 2,500 per square inch of skin) over a softer, finer, twisting, woolly underfur (approximately 12,500 hairs per square inch).

Guard hairs absorb solar energy and create still-air spaces, helping with heat retention. The underfur provides even more insulation. Half the length of guard hairs, underfur is five times as dense. For comparison, sheep underfur is only four times as dense. The underfur traps layers of air, with warmer layers closer to the skin.

Deer can further increase the insulating function of their fur by raising their hair. Each hair follicle is connected to a tiny bundle of skin muscles called arrector pili. In response to cold, these muscles contract causing the hair to stand on end — just like our “goose bumps.” This results in a thicker layer of insulation and more still air spaces. In effect, deer grow their own adjustable insulating blankets anew each autumn. These blankets are so effective that falling snow can accumulate on a deer’s back.

Black-capped chickadees, those tiny bundles of feathers, are active here all winter. They depend on their high metabolism rate to maintain body temperature (over 107 degrees), their body processes fueled by food. They spend as few as four hours each day locating and eating fat- and protein-rich insect larvae and eggs, plus some seeds when available, during the winter.

At night they slip into a tree cavity, usually singly but occasionally in small groups. Once settled down they gradually enter “regulated hypothermia,” reducing their body temperature by up to 20 degrees in order to conserve energy resources to make it through the night without feeding. Amazingly, almost all of the subcutaneous fat a chickadee has stored as it goes to roost at the end of a winter day will typically be used up during the night. When sunrise arrives they are up and out and searching again for food and fuel.

Chickadees travel in communal flocks, together with other chickadees, nuthatches, titmice, small woodpeckers, brown creepers and golden-crowned kinglets. These mixed-species flocks enable all the participants to concentrate on locating food. They delegate predator watches to the group as a whole. Many aware eyes mean more vigilance for danger. They communicate their flock positions through soft, hard-to-localize vocalizations and listening, enabling more visual focus on locating food.

They avoid competition for food sources, even though they feed together on the same foods, by different searching behaviors and specific niches in the trees; chickadees out in the smaller branches, nuthatches hitching down the trunks and major branches, creepers spiraling up the trunks, woodpeckers hammering through bark to wood below, kinglets primarily in evergreens. A very neat and cooperative division of responsibilities.

In the next “Earth Matters” I’ll discuss how we imitate these creatures to keep ourselves comfortable in the snow and cold.

Ted Watt is an educator/naturalist at the Hitchcock Center for the Environment.

Earth Matters, written by staff and associates of the Hitchcock Center for the Environment at 845 West St., Amherst, appears every other week in the Daily Hampshire Gazette. For more information, call 413-256-6006, or write to us.

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