By Elizabeth Farnsworth Gazette Contributing Partner
As far as I can tell, there are three ways to survive a New England winter. One, you take up winter sports and learn to love the slippery ground and nose-biting cold. (This one’s not for me—I am too clumsy for skates or snowboards.) Two, you escape to warmer climes. (As a tropical biologist early in my career, I opted for this, and spent many winter months knee-deep in mangrove mud in Belize; not glamorous, perhaps, but warm!) Or three, sleep through it. Many animals and plants choose option three: it’s cheaper than airfare or new skis.
Since the Valley received a wallop of an early winter in October, it seems timely to talk about how organisms slow down and go dormant, oblivious as the snow flies. Bears do it, bees do it, even trees do it! We humans are learning much about our own biological clocks and metabolism by studying the hibernation habits of other species.
Think of hibernation, and you may think of a black bear (Ursus americanus) curling up in its den. Actually, bears are quite light sleepers, even though their metabolism changes dramatically during the denning period. The core body temperature drops about 10oF, and the heart rate slows from a resting rate of 40 beats per minute to only eight or so. Most bears will not drink water for months, and their only source of calories will be the pounds of fat they accrued during summer— as much as 30 pounds per week; scientists note that there’s no such thing as “bad” cholesterol for a bear. Yet, a mama bear will rouse herself during the winter to give birth to one or two cubs, who nurse even as she slumbers on. (Interestingly, the fertilized egg of a bear itself can enter a state of suspended animation, not implanting in the uterus and developing until the mama gives the hormonal go-ahead.) Bears are busier than we think.
Other New England mammals such as chipmunks, squirrels, and bats also doze through the winter months, their body temperatures dropping close to 40 degrees, similar to their surroundings. However, they, too, periodically stir from this torpor, drinking, feeding lightly on stored food or warming up their body fat reserves. Wake too often, however, and an animal can use up its calories before spring. One of the deadly effects of white-nose syndrome, the fungal disease killing bats throughout the eastern U. S., is to frequently awaken bats by irritating their skin. Flying during the winter, the bats freeze or become seriously malnourished.
Snakes also enter a quiet period called brumation. This is not sleep in the true sense, but does involve a significant slowdown. After feeding heavily in late summer, our native garter snakes gather in large groups in a chamber called a hibernaculum. Hundreds of cozy, coiled reptiles can stay a bit warmer than a single snake, even when they can’t generate their own body heat, so the hibernaculum temperature stays above freezing. The hibernaculum heats up only slowly in the spring, though, and snakes remain clumped together until the weather warms. I once startled a hibernaculum of dozens of knotted-up garters under an old pallet in early June.
And what happens to ants, flies, grasshoppers, and other insects in winter? Most die, but others, such as ant queens, must stay alive by cuddling up with some workers deep in secure nests below the frost line in order to produce a new generation in the spring. Some insects enter a period of inactivity called diapause, which arrests their development in a particular stage until environmental conditions become favorable for them to mature. Monarch butterflies, for example, coalesce together in enormous, lethargic groups in their wintering grounds in Mexico and California, delaying the onset of their ability to reproduce until they return to their summer feeding grounds in our New England fields.
Our champion winter nappers, of course, are plants, though you’ll never hear them snore. In response to dropping temperature and shortening days, trees and shrubs “harden off” their tissues by preparing their cells to lose water and endure freezing in a complex hormonal process. And seeds are the most impressive of all, with many able to suspend growth for years until the time is right to germinate. The record-holder for dormancy is a lotus seed that germinated after 1,300 years of dormancy.
May this winter not last that long!
Elizabeth Farnsworth is Senior Research Ecologist at the New England Wild Flower Society, and scientific illustrator of the recently released Flora Novae Angliae (Yale University Press). Regular readers of this column may note that she published an article on Valley nap-spots, but she assures readers that she actually does a few things other than sleeping.
Earth Matters, written by staff and associates of the Hitchcock Center for the Environment at 525 South Pleasant St., Amherst, appears every other week. For more information, call 413-256-6006, or write to us.Click here to return to full list of Earth Matters articles.