Deer, foxes, rabbits, etc. are all warm blooded mammals that regularly experience sub-freezing temperatures that would kill humans in a matter of hours. How do they survive?
In: 1817
I wish I could answer with one word!
Endothermy.
We mammals run hot. With insulation and burning calories we’re always warm and a high metabolic rate.
Other adaptations help too but it’s mostly the first thing. Exothermic animals rely on antifreeze or high ammonia blood.
One of the most under-appreciated answers is **brown fat.** Brown fat is a lot like body fat, but it has nerves. When signaled by the brain or spine or whatever, these special fat cells start burning calories. They’re not doing work in the conventional sense, so all the calories they’re burning are released in the form of heat applied directly inside the body and bloodstream.
Its presence in humans was thought to be limited to babies, but more recent studies have found that it lingers to some extent later in life, this is determined by your genes, and the proportion of brown fat you retain is inversely correlated to obesity.
“Warm blooded” means that they generate their own heat, typically in excess. They are their own little space heaters.
They also all have fur that’s very good at insulating them, a hide much thicker than our skin that’s also a good insulator, and natural oils that do a good job of making their fur rather waterproof. This helps keep the heat that they generate in their bodies.
These animals also have a seasonal coat. My dog is shedding like mad right now as she replaces her summer coat with her winter coat. In the winter they have thicker coats that are better at retaining heat.
Related to the seasonal coat is normal acclimatization. All animals are capable of acclimatizing to an extent, and northern mammals are pretty damn good at acclimatizing to cold winters. Their metabolism changes, their fur and hide changes, their circulatory system adapts.
It’s literally the same for us by the way. We acclimatize to hot and cold conditions, but a lot of our natural acclimatization is hindered by the fact that we spend most of our time in climate controlled dwellings, especially in the winter. When you’re warm all day in a heated office and warm all night in your heated home, it’s hard to acclimatize yourself. The more time you spend outdoors in the cold though, the more resilient you become to it. The exact same is true for working in hot conditions. You’re more likely to experience heat stress if you just jump right into hot work one day compared to someone who gradually spends more and more time working in the heat and builds a tolerance to it. Because we coddle ourselves indoors, we suffer outdoors. However if you spend more time outdoors, the winter won’t be as bad.
Most of these mammals also dig dens for shelter. Yes, even deer. This gets them out of the wind, so that when they settle down for the night they can stay mostly out of the wind and their thickest fur on their back can insulate their topside while their underside is tucked away and cozy. You’ve probably also noticed how neatly most animals can curl into a ball. Way better than us. This lets them fit into smaller dens and protect more of their bodies from the elements.
Lastly, diet and metabolism. Many of these animals tend to store fat as they acclimatize to colder weather. They were outside all autumn, which means they were able to adapt gradually. Some of these animals have a rather steady supply of food through the winter too. Many of these animals are just *always eating*. They need the constant supply of energy to stay warm. When they’re not eating, they’re resting for as much of the day as possible to conserve energy.
Winter food sources are a major, if not the biggest limitation to a species local population. When deer run out of food to eat, they freeze to death, and humans can have a devastating effect on this. If an area that used to be able to support 1000 deer gets ploughed for human development and can now only support 500, the deer don’t get the memo. It’s not like 500 deer move out in October so that the other 500 can eat through the winter. They all stay, and they all try to survive through January, February and March. They end up running low on food sources halfway through the season though and then they start scattering looking for more food. Many die. Because 1000 deer can’t go two months without food, the population can end up collapsing and far more than 500 die off. The survivors are ones who left for more food and were able to scrape by. The region ends up being left with less than 100 deer. This is actually why hunting can be important. If we keep track of deer populations through the year, then we can sell 500 deer tags. Hunters go out and get their 500 deer, and the remaining 500 actually have enough food to get through the year, and the region keeps 500 deer.
We wouldn’t have to hunt if we didn’t drive off their predators too. But we tend to not not be compatible with wolves hanging around developed areas, so they’re the first to get scared off.
When we wrap it all up, wild animals have developed the evolutionary traits that they need to survive the winter. So long as we don’t throw things out of balance for them (like their food sources or predator population), most of them will find enough to eat to keep their bodies warm.
Humans on the other hand gave up most of those evolutionary traits millennia ago in favor of big brains, opposable thumbs, and communication. This lets us form social networks or “tribes” that work together to achieve goals, create and build solutions to our problems (coats, huts, etc), and most importantly of all, create things that benefit more than one generation. That’s not only to say that building a house keeps the next generation warm. Our communication also allows one person to discover or invent a technology, and our entire society or civilization can benefit from it. We have dens and thick coats too, we just had to make them ourselves.
Simple answer is that some do die. Survival of the fittest (natural selection, or evolution) has acted on animals for countless generations, so the ones who exist are ones that had good fur and other features making it so they deal well with cold conditions (the ones that did not, died, and they have no descendants to suffer the same fate for the same reasons, for having inadequate fur or whatever). There will always be some that die by accident, bad luck, or some random thing or another, but mostly they have the features and behaviors that favor survival. Nature has forced them to be able to survive the conditions, and only the ones that can, do survive, or we would not have ANY such animals around (nature would have killed them off long ago). They exist today because they have features that help them survive nasty conditions.
Like humans, many mammals hide out when the weather gets too extreme for them. They find safe spots, such as burrows or caves, or dense pine forest zones that offer protection from exposure, and they stay there in relative warmth (they make themselves animal equivalents to tents or igloos or whatever using natural materials, just like a human used to living in the wild would do).
Wild animals expect bad conditions and actually are prepared and know how to deal with them (they do not know any other life). Humans have forgotten, as a general thing, so when we get stuck, unexpectedly, out in the wild in nasty conditions, we tend to die, which is why so many of us avoid nasty conditions. We don’t want to die from being stupid or from our lack of knowledge.
Not many of us have the skills and knowledge that was once needed to survive away from the house (I would not survive one winter as a fur trapper, for example), so we don’t go away from the house. And when we do by accident or stupidity, we tend to die.
What do you do when it’s cold?
Put on a coat or stay inside.
Animals already have the coat part figured out, so they find a warmish(er) place and hangout, ensuring to take up the smallest surface area to preserve warmth.
And, if your animal is absolutely psycho nuts like my dog, they’ll run full tilt around the property at -40 to generate warmth.
Wild animals don’t do this though. Movement = Energy, Energy = Food, so Movement = Food and there’s no garauntee of rhe next meal.
Worked with a guiding company and it’s worth noting that plenty of mammals do freeze to death. Cold = death.
That said, yes it’s mindboggling just how astonishingly weak humans are in comparison to most mammals. Even if you tried to mimic them (we sure do, we literally physically remove their skin and put it on) and most of us would still be dead soon.
Anyway, I’m told, in part, this is ‘in part’ but most non-human mammals also have a different kind of muscle array. So never mind the fat and fur, this is the actual muscles is woven in a way that may also trap and contain heat way better than humans.
To me the most amazing question is how are humans so incredibly weak and fragile compared to those mammals. We’re the freak and weak thing after all.
Oh’ I know the answer!
Their fat is different from ours.
We have “white fat” (yellow) and it’s not the type of fat that would keep you warm if you were a bear or a deer.
They have “brown fat” which is made to keep them warm as warm blooded creatures.
It doesn’t mean they don’t freeze, but that with huddling together and creating nests, they have a higher likelihood of survival
A lot of methods, sometimes in combination.
Some flock together to share body heat. For reference I’ve seen on documentary that a flock of penguins in the Antarctic can reach up to 45 degrees C in the middle just by being close to each other, the middle guys start boiling alive and the flock has to constantly shift so the freezing outer guys get some heat and the boiling inner guys cool off at the edge, it’s a brilliant tactic for social animals. (I had guinea pigs and they do this, it’s always surprising how hot it gets)
Larger animals lose heat far slower than small animals so can usually survive without having to flock, but they do seek shelter from wind and rain/snow which would accelerate the loss of heat – natural caves, mounds, thick brush can all do the trick.
Smaller, solitary animals dig burrows or find natural shelter, very often solid ground or a pile of leaves can be surprisingly insulating and the temperature underground is more tolerable than surface temp, and snow is also very insulating depending on the air content (think igloos) so a snowy ground wouldnt be that bad for anything under the soil. Foxes and kitties tend to curl up into a ball and use their tail as insulation for their tucked-in extremities.
Some animals hibernate because they’re just too small to retain their body heat and can’t find enough food to keep their internal fire going. Big animals can hibernate too, mostly from lack of winter food, though heat usually isn’t an issue.
Some animals specifically shed a light summer coat for a thick winter coat of fur when the weather turns cold, and the nature of fur keeps their skin warm and dry, even if the fur is tipped with snow/ice. (Furred animals have a very soft downy layer by their skin which traps heat, and a coarser outer layer to catch precipitation and keep the downy layer dry – if the downy layer gets wet it is rendered useless and actually draws heat from the animal even faster, an animal falling into an icy body of water has very little chance)
Having enough body fat going into the cold season makes a huge difference for any warm blooded animal, for both insulation and metabolic fuel. Preparing by eating excess when it’s warm is common. If food is not an issue in winter, the animals simply eat more and move more, they shiver and expend energy to generate more heat. (All warm blooded animals shiver but the ones that stay fed don’t deplete their fuel). Squirrels are a good example of an animal that ensures it has winter food.
Let’s not forget a lot of birds and rodents have adapted to live in human housing, and as we make sure to keep ourselves warm, the animals take advantage of the readily available warm shelter. Insects can also do this to avoid the frost which usually does kill them as they’re not warm blooded.
I know it’s not a mammal, but there’s a frog that can technically be completely frozen by frost, but will survive when thawed. I can’t remember what species but some animals produce a natural antifreeze in their blood that lowers the freezing point in their body, so fluids can still circulate even if the body is directly in contact with icy conditions.
Some birds and mammals migrate to somewhere warmer, simple solution.
It’s wild how so many animals have so many methods for avoiding freezing to death but as it’s a life and death thing, adaptations are sure to emerge.
Despite everything, sometimes it’s just not enough and a lot of animals do perish from the cold.
Many animals also use hibernation and torpor to deal with cold temperatures. I.e. controlled hypothermia
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