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Adaptation, forms of hibernation help non-migratory animals survive our Berkshire winters

Black-capped chickadee on a branch

Birds, like the black-capped chickadees, grow more feathers than usual in the winter. The feathers give them the ability to fluff them to trap body heat.

One of the most wondered — yet rarely asked — questions this time of the year is how do animals that don’t migrate to warmer climates manage to survive? (Like some of our friends, including J. Randy and Jackie, and Joyce have done.)

It isn’t often more difficult than it sounds, and difficult as it is, most animals are able to survive, ready to get on with life, mate and to raise the next generation. And here is what I know, far from the complete story, but more an outline:

OUR WINTERS ARE GENTLER now than it seems to me the past were. And most of the animals staying in the north must put up with the outdoors, finding enough food to keep warm, while others hibernate or hole up in a burrow and spend much of the winter in torpor (sleeping), waking now and then for a stored meal. The easier winter may be the reason for some species once found only in the south, like the cardinal, mockingbird, Carolina wren, red-breasted woodpecker and others.

Animals do manage through our winters and have in the past. For me, even more exciting than birds, mammals, amphibians and reptiles, I am fascinated that some frogs can freeze while in brumation by making a type of antifreeze, a form of sugar alcohol in the bloodstream. Strangely, something similar happens in the mourning cloak, giving it the opportunity of being the first butterfly of the spring here.

Birds adopt various tricks, better called adaptations, that allow them to survive. One is growing more than usual feathers and the ability to fluff them to trap body heat. Some, like our Eastern bluebirds, spend the frigid nights huddled together reducing heat loss. In earlier NatureWatch columns, mention has been made of some bluebirds making use of nest boxes to avoid the wind, and gathering in a nest box in a group providing even more warmth. Some black-capped chickadees may also use nest boxes or cavities.

A bird's naked legs and feet often make us wonder, especially those of ducks. We may wonder why they don't freeze? Their legs and feet have very little blood flow and muscle, having little heat to lose. Sometimes we might see ducks in the winter tucking one foot up close to the body for warmth, each taking a turn. Some larger waterfowl and gulls have something called countercurrent, meaning the arteries and veins run close to each other in the legs, allowing warm blood from the heart heat the cold blood from the feet. This keeps them from freezing while standing on ice.

Mammals have ways to keep from freezing, and most grow more fur for the winter. And some will, like bluebirds in a way, huddle among their own for warmth. Some search out others for warmth, like otters joining beavers or muskrats in their dens. Gray squirrels return to their nests or cavities for food and warmth, and except for warm days, spend much time sleeping. The same is true of chipmunks, and if you wonder why they store so much food in the fall, now you know. Woodchucks and bats hibernate, while our bears, having fattened up for the “long winter’s nap” enter a mild torpor (not hibernation, that is a very deep dormancy) as does the woodchuck.

Both land and aquatic frogs neither hibernate nor enter torpor; they brumate. Terrestrial frogs and some turtles find below freezing places, like deep under leaves and in deep dens below freezing. In the case of snakes, it is deep dens below the frost line. Although common garter snakes are known to search out dirt cellars.

Most turtles winter in ponds and lakes, even rivers, and spend the winter buried in mud at the bottom. Not all though: Back when I was actively "head starting" the rare and endangered red-bellied cooter (turtle), Terry Graham, then professor at Worcester State University, often discussed the species and his discovery of just how close to the loss of the Plymouth population of this turtle we were, told me of his below-ice exploration of one of the ponds where the species lived. In scuba gear, he swam just above them; they weren’t under the mud, and some were actively walking about. Hence, not all turtles necessarily go into torpor, and you may even see turtles moving around under the ice on winter days.


Q: I’m seeing more bluebirds this winter than in the past. A couple at my feeders (mostly at the suet). Saw what can only be described as a flock at the Rockwell Museum. Is this common this year throughout the region? Are they becoming more common residents?

— Mike H., Becket

A: Yes, these lovely birds are increasing, probably, for one reason, there are more nesting boxes all the time.


Thom Smith, NatureWatch columnist.

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