Published Dec 1st, 2019
The animals who overwinter in and around Norwich show us many adaptations for survival. Unlike those who leave for the season, some arrive from less habitable spots. We’ll look at some winter voyagers as well how creatures use simple behavior changes; take a biological “time out” reset bodily thermostats; and change coats for warmth or a new seasonal color.
A careful observer might also see elaborate nest building, insulating burrows, a switch to higher-calorie prey, and the fascinating patterns of food hoarding, which can put specialized memory tricks on display.
Animals move with the seasonsin search of warmth, food, or other benefits, some leaving and some arriving. The Common Loon will leave our area not to fly south, but east to the Atlantic coast with its open waters and bountiful fishing. Meanwhile the Common Redpoll and the Pine Grosbeak, summer denizens of far northern forests, pop up this far south from time to time. That’s called “irruptive” migration and its causes aren’t fully understood, although food plays a role. The redpole needs birch and alder seeds; the grosbeak seeks fruit, especially berries of the Mountain Ash.
The tiny Golden-Crowned Kinglet, like many other birds, fluffs its feathers and tucks its head deep under the ones on its back to stay warm at night. And several of them huddle together, which reduces heat loss by 23 percent for two birds and 37 percent for a group of three.
Diapause means a period of arrested development – suspended animation. The Eastern Black Swallow butterfly’s latest generation of caterpillar, arriving with autumn’s chill, overwinters as a chrysalis in its cocoon to emerge and unfurl its new wings in the spring. This “time out” avoids freezing and starvation.
Hibernation and Torpor
Don’t oversimplify these complex patterns, which most of us associate with bears. Their famous hibernations are one form of torpor, which we can see in skunks and woodchucks too.
Torpors are complex and highly variable alterations of physiology, in which many animals reduce their activity – mainly body temperature and metabolic rate, or energy production. Some bouts of torpor come and go in a day; others may last a week or more. Animals come in and out of torpor on a regular basis all winter long, because it’s costly to maintain this state.
An animal that cycles in and out daily is called a thermoregulator; one whose torpor goes on for many days is a hibernator.
The striped skunk, a heterotherm, may go into its den as an individual or in a group. A loner’s torpor may last 8 hours and it can get as chilly as 80 degrees. In a group, torpor lasts about five hours and rarely goes below a body temperature of 88 degrees. That’s called social thermoregulation.
Woodchucks, by comparison are hibernators, their torpors lasting up to eight days at a time, and their temperatures falling as low as 38 degrees.
Camouflage and Insulation
Short- and long-tailed weasels are among our town’s residents whose coats change from mostly brown to white in winter, the better to blend into the snow and ice. There’s a double benefit: the shafts of the winter fur, are structured to trap more air in a fluffier warm layer, at the same time this reflects more light and emphasizes the whiteness of the coat.
For more information, books at the town library include Winter World by Bernd Heinrich and Life in the Cold by Peter Marchand.
Originally published in Holiday 2019 Norwich Times