If you are going out in this bitter weather, you’ll need many layers of insulation to protect your relatively fur-less self from the wind and cold. Wildlife are out in the weather all of the time and a hard winter can be hard on them as well, so when does the cold start to get to them?
The answer to this question lies in the concept of thermoneutrality. You are thermoneutral when you can go out in your birthday suit and not have to use energy to heat or cool yourself. For humans, this is a relatively tropical 79 to 82.5 ℉. Wildlife have the benefit of fur, feathers, fat, specialized circulatory systems, and, for ungulates, the heat created by digesting roughage, but they aren’t immune to the cold. Finding thermoneutral temperatures for wild critters does pose some unique research challenges because live moose generally don’t want to go into a walk-in freezer for science. Here are our best estimates of when different species start to feel the cold:
Cold weather specialists:
- Bison put on thick hairy coats and the thermostat has to hit -40℉ before they start to expend more energy to keep warm.
- Moose are unbothered down to -9 ℉ and may even get too hot if winter temperatures top 20℉.
- Mule deer don’t start to shiver until it’s down to -4℉ although they are more flexible than their other compatriots and can handle heat up to 41℉ in their winter coats.
Pretty dang tough:
- Trout can handle water temperatures down to 35℉ and below 32℉, well, the water’s a bit too hard for them.
- Coyotes and snowshoe hares can deal with subfreezing temps pretty well, although they have to kick in the afterburners at about 14℉.
- Wolves can go a little cooler at around 10℉.
- Pronghorn may not be cold proof as the deer species, but they are fine until 12℉.
They’re already shivering:
- Voles start to get chilly when the temps get below 68℉, so how do they stay active all winter? They have some protection from their tunnels and burrows, but mostly, they have to eat a lot to fuel their little bodies and they store food for this purpose in their burrows.
- Chickadees catch a chill as soon as the weather gets below freezing. They also rely on food stores to keep them warm through the winter, hiding and remembering the location of up to 5,000 pieces of food per day. They can also lower their body temperature at night, but they still end up burning through up to 40% of their body mass on a cold night.
In the end, winter stress is generally not due to the cold itself, but to snow and other weather factors, which make movement and finding food more difficult. Snowpack is a much more accurate predictor of winter survival than winter temperatures.