BIG CHILL? NO PROBLEM
Postmedia’s Tom Spears looks at snow and ice and wildlife to see what makes our coldest season tick. Today, why tiny animals don’t turn into tiny ice cubes when the temperature falls.
As you stand in cold of -25C, it’s easy to feel pity for chickadees that weigh only a few grams, and can’t come in from the cold at night. Don’t bother. They’re fine. So are the other small birds and animals in winter — grey jays, sparrows, squirrels, voles, chipmunks and the rest, each of which has a strategy that works as well for them as down coats and heavy boots do for us.
Chickadees burn much of their body weight each night and fatten up each day.
“Mammals use fat on their bodies as insulation to stay warm, while birds burn it for energy,” says Mike Runtz, a veteran naturalist who teaches biology at Carleton University. Chickadees actually have a slightly warmer body temperature than ours — except on cold nights, when they and some other small birds go into a state of “torpor” — dropping their body temperature and slowing their heartbeat. It’s sort of midway to hibernation.
When the sun rises, they hunt for food again, refuelling the fire.
Chickadees also shiver. In humans that’s a sign of trouble, but the bird vibrates its big flight muscles as a way of generating warmth.
Chickadees are good at finding high-calorie food. They’re seed eaters, so they love sunflower seeds (high in oil, which is wonderful winter food). Suet is also good for many bird species in winter. Runtz’s homemade mix is lard and peanut butter.
Ruffed grouse dive into snowbanks and use the snow as a blanket at night. So do redpolls.
Small mammals exploit the multiple layers in snow for warmth.
“There is a layer next to the ground called the subnivean space. When the snow gets thicker and thicker, the stuff next to the ground becomes more crystallized because of the latent warmth in the ground.”
It provides, in effect, a warm hideaway only one to two degrees below the freezing point. It’s good for small mammals and even spiders.
Humans put on a winter coat over a sweater. So do animals.
“Birds that stay behind (in winter) put on two layers.” The outer layer of “contour” feathers grows thicker in fall, and it keeps out the snow and breaks the wind. The inner downy layer also grows thicker. It stays dry and provides insulation.
“Same for mammals, too. Mammals have the long guard (outer) hairs grow longer and denser in the fall, and under that is their longjohn system, the under-fur that also gets denser.”
If there’s snow on a squirrel’s fur, that’s actually a good sign, Runtz says — it shows the animal has been digging up food.
Hibernation is much more rare than people think. Many animals become lethargic in winter — black bears, bats, raccoons — but don’t truly hibernate.
True hibernators such as groundhogs, meadow jumping mice and woodland jumping mice all drop their heart rate and body temperature down to a near-death level, and stay like that for months.
Bears and others, however, don’t go that far. Bears drop their heart rate to about eight beats per minute, but their body temperature stays close to normal. Don’t poke one with a stick, because it can rouse itself. Also, its babies are born in January.
“That’s why on really warm days in winter there will be things like raccoons active, and skunks,” Runtz says.
Small animals are good at finding shelter, ranging from holes in trees made by woodpeckers (good for small birds) to bigger tree cavities (squirrels and raccoons) to attics and garages. Some (deer mice, flying squirrels) also huddle in dens to share warmth and reduce their surface area.
“The activity at my feeder was fantastic this morning,” Runtz said one cold December morning. “I’ve got a red-bellied woodpecker, a red-breasted nuthatch, which I hadn’t seen this winter, and about 50 juncos and some tree sparrows. It’s really lovely.
“That’s one thing I like about winter — getting out on a cold morning. Birds take a little time to get active … but once that sun comes up there’s a great surge of motion and sound as these things come to life and start to fatten up for the next night.”