Wintertime brings a silence to the forests cradling the Vail Valley, and it’s not just the hush of new-fallen snow. By September, most of the critters that liven the summer months with their treetop chattering and raids of hikers’ day packs have vanished.
But not all are spending the season basking in tropical sun, snickering about the poor saps they left behind. Many of the valley’s furry residents are right beneath your feet ” or skis, or snowboard ” hibernating far below the snow’s surface.
To the working stiff, the life of the hibernator sounds enviable. Spend the most pleasant half of the year gorging yourself, and just as the weather turns nasty, go to sleep for the rest of the year. When you awake, magically, you will have lost nearly all the weight you gained and it’ll be time to start eating again. No work, no dieting, just food and sleep.
Alas, it isn’t that simple. In fact, the more you learn about hibernating, the less appealing it sounds.
Marmots, chipmunks and ground squirrels are examples of some of the area’s “true” hibernators (more on that later). But just because they’re out of sight beneath the snow all winter, “That doesn’t mean that they’re asleep in their burrow,” says Colorado State University professor and hibernation researcher Dr. Gregory Florant.
People commonly think of hibernation as the equivalent of a very long winter’s nap, when in fact rodents like marmots and ground squirrels go in and out of sleeping and waking periods, Florant says. During the sleeping ” or torpor ” state, their body temperatures drop to the near-ambient temperature, often barely above freezing. (Not such a cozy nap, after all.) Their heart rate and breathing slows accordingly, and they become very difficult to rouse.
“This is of course a big energy-saving mechanism,” Florant says.
Every five to 10 days, however, the rodents will rewarm themselves and spend a few hours awake in their burrow before slipping back into torpor. The cycle continues until warmer weather arrives, when their urge to reproduce sends them from their burrows in search of their version of Spring Break.
Other animals, like bears, have hibernation habits that aren’t quite so structured ” and some scientists question if they are even actually hibernating.
“There is a little bit of debate on what a true hibernator is,” says Keith Giezentanner, White River National Forest wildlife program leader. He doesn’t consider bears true hibernators, instead calling their winter coping mechanism “dormancy.”
When bears enter their dens, they won’t necessarily stay there for the entire winter as the rodents do in their burrows. Because they drop their body temperatures much less dramatically than their buck-toothed counterparts ” only about 10 degrees Fahrenheit less than normal ” bears aren’t as soundly asleep, even in the depth of their dormancy.
“They’re in a deep sleep, but they can arouse much (more easily),” Florant says.
As a result, bears can periodically be found outside their dens during the winter or on warmer early spring days, and researchers often must tranquilize bears if they enter a den to study the bear, Giezentanner says.
Furry animals aren’t the only ones who hunker down for winter in the valley. Amphibians, reptiles and even insects have their own methods of letting winter go by without them.
Since they cannot regulate their body temperature, frogs, toads, snakes and lizards must find a place to hibernate that will be warmer than the outside air, such as mud at a the bottom of a pond or the base of a rock pile. The boreal toad, a rare High Country resident, will hop as far as a mile and a half from its wetland breeding grounds to find a suitable rock pile in which to spend the winter, Giezentanner says.
The mountain pine beetle, which has killed many of the area’s lodgepole pines by targeting trees weakened by drought, age or other factors, has evolved an equally devious way of surviving the winter. At the outset of cold weather, the beetles turn some of their blood sugar into ethylene glycol, which is a primary ingredient in antifreeze, Giezentanner says. The conversion enables them to survive temperatures 40 degrees below zero for several days, he says, which they are unlikely to encounter tucked between the bark and wood of their host trees.
For we humans, the main concern of a dry autumn ” like what the valley experienced this year ” is the lost time on the mountain and the resultant effects on the economy. But for hibernators, it can be a matter of life and death.
Rodents dig their burrows two to three meters below the frostline, Florant says. There, soil is a fairly constant temperature in the 50s, Giezentanner says. The frostline can drop lower than normal if there isn’t enough snow on the ground to insulate the soil from colder air temperatures.
Giezentanner doesn’t expect this year’s weather to have much of an effect on local wildlife populations.
“That’s not something that’s never happened before,” he says.
But if the worldwide warming trend continues as scientists expect it to, Florant does foresee harmful effects on hibernators, such as changes in the timing and depth of hibernation.
“I think it is going to impact their hibernation patterns,” he says. “We’ll just have to see over the long run.”
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