“If the covers could be taken off the fields and woods at this season, how many interesting facts of natural history would be revealed! – the crickets, ants, bees, reptiles, animals, and, for aught I know, the spiders and flies asleep or getting ready to sleep in their winter dormitories; the fires of life banked up and burning just enough to keep the spark over till spring.”
— John Burroughs, 1924
I’d say I am prepared for the winter. I’ve got heated seats, beanies for cold days, and I’m pretty sure the neighbors have been eyeing my woodpile. But it makes me wonder, how does wildlife do it?
Local animals have been working diligently to get ready for the cold. As the temperature drops, warm-blooded animals struggle to maintain their body heat while balancing their energy stores. Using too much energy will result in death, which means it is time to shape up or ship out. Their survival depends upon the proper preparations.
Fur, fat and feathers
Fall becomes a time of feasting and foraging to prepare a nice fat base layer. This fall happened to be a good season for berries, so our black bears didn’t have to work as hard for their necessary 20,000 to 30,000 calories per day. This all goes toward their insulation, a snug 5 inches of fat underneath their dense fur.
Fur and feathers multiply or change color to maximize heat retention and camouflage. Ptarmigans put on feathered leggings, and start their gradual transition to snow-white winter coats, alongside snowshoe hares and weasels. Meanwhile, deer shed their fur for a thick gray winter coat, equipped with insulating under fur and longer guard hairs (hollow hairs which trap air like a down jacket).
This coat may be sufficient to protect the animal all the way down to 50 degrees below zero. But, trying to maintain a normal body temperature in exposed winter conditions can still be a challenge.
Sleep it off
For most mammals, the key to survival is to conserve energy. One way the body does this is by creating thermal equilibrium with its surroundings and stopping heat loss. However, when temperatures get low enough, the mammalian nervous system cannot function (think hypothermia), so the system shuts down into a vegetative state called hibernation.
This survival technique is regulated by day length and hormone changes. Heart rate slows, while the other bodily functions sluggishly keep pace. Keeping their internal thermostats just above freezing, hibernating animals can be poked and prodded without being roused. To be in such a vulnerable position, animals have to prepare state of the art security dens, or sealed off burrows called hibernaculas. Snow is a good insulator — so these hibernaculas may be a cozy 33 degrees while the air dips below zero.
Burrowing under the snowpack is an option open to smaller animals like mice, voles, and pocket gophers, whose size allows them to make use of this area called the subnivean zone. Even smaller organisms, like insects for example, cannot generate enough heat to do anything else but spend the winter as fertilized eggs, larvae or hibernate.
Let’s just go to Mexico
If you want to escape the winter weather altogether and have more room to breed, then migration is feasible, but only if you’ve got wings. Flying doesn’t require too much energy, especially for lightweight birds that can pack in high-density fat stores. Routes vary from species to species. Our pint-sized broad tailed hummingbirds make the perilous trip alone, not in a flock, crossing the Gulf of Mexico in one continuous 18-hour flight to their winter destination in the mountains of Mexico. For most mammals though, migration is too energy intensive and is left to our large Rocky Mountain ungulates such as the elk.
Most people give very little thought to the intricacies of winter life. But next time you hit the slopes, if you stop and listen, then you might notice some amazing things. Although it may seem silent with snow, listen to the crack of evergreens splitting from water in the trunk freezing. And the chiseling of the woodpecker, hunting for pine beetles, that make their own anti-freeze. With all the different evolutionary innovations and strategies for survival, winter is truly a wonderland.
Brittany Bobola is a multi-season naturalist at Walking Mountains Science Center. Come join her for a nature walk Mondays through Saturdays daily at 2 p.m. to learn more about our winter wonderland.