Is winter miserable for wildlife?


While the weather outside may actually become awful this winter, a parka, a knit hat, woolen socks, insulating boots and perhaps a roaring fire make things bearable for people living in cold climates. But what about all the wildlife there? Will not they freeze?

Pets are often combined with protection against the cold.
Photology1971 /

Anyone who walks his dog when the weather is cold knows that dogs will tremble and prefer a cold paw – which partly explains the boom in the pet clothing industry. But chipmunks and cardinals do not have trendy coats or boots.

In fact, wild animals can succumb to frostbite and hypothermia, just like humans and pets. In the northern United States, unpacked opossum tails are a common victim of cold exposure. From time to time, an unusual cold spell in Florida results in iguanas falling from trees and manatees dying as a result of cold stress.

Avoid the cold is important to preserve life or limb (or, in the case of possum, tail) and the possibility of recurring. These biological imperatives mean that the fauna must be able to be cold in order to avoid the harmful effects of its extremes. Animal species have their own equivalent to what humans feel as an unpleasant bite mixed with a needle pin sensation that drives us to warm up quickly or suffer the consequences. In fact, the mechanisms of the nervous system to detect a range of temperatures are virtually the same in all vertebrates.

A winter challenge for warm-blooded animals, or endotherms, as is known scientifically, is to maintain the internal temperature of their bodies in cold weather. Interestingly, the temperature detection thresholds may vary depending on the physiology. For example, a cold-blooded frog – that is, ectothermic – will feel cold from a lower temperature than that of a mouse. Recent research shows that hibernating mammals, such as the 13-line ground squirrel, feel cold only when temperatures are lower than endotherms that do not hibernate.

The animals know when it is cold, at different temperatures. When the mercury collapses, does the wildlife suffer or go with the icy flow?

Some animals find a protected place to wait for the worst, like this chipmunk.
Michael Himbeault, CC BY

One solution: slow down and check

Many cold weather endotherms have a sluggishness: a state of reduced activity. They seem to sleep. Because torporous animals alternate between regulating their body temperature and allowing the environment to influence it, scientists regard them as "heterotherms". In difficult conditions, this flexibility offers the advantage of a lower body temperature – remarkably in some species, even below the freezing point at 32 degrees Fahrenheit – incompatible with many physiological functions. The result is a lower metabolic rate, and therefore a lower energy and food demand. Hibernation is an extended version of the torpor.

Torpor has advantages in terms of energy conservation, especially for smaller species such as bats, songbirds and rodents. They naturally lose heat faster because the surface of their body is large compared to their overall size. To maintain their body temperature in the normal range, they have to spend more energy compared to a bigger animal. This is especially true for birds that maintain average body temperatures higher than those of mammals.

Unfortunately, torpor is not an ideal solution for surviving in freezing conditions, as it involves trade-offs, such as a higher risk of becoming another animal's meal.

Adaptations that help

Not surprisingly, the animals have developed other adaptations to withstand the winter months.

The big ears of a fennec fox would be a handicap in a cold climate like that where the arctic fox lives.
Jonatan Pie / Unsplash and the Kkonstan / Wikimedia Commons, CC BY

Wildlife species in northern latitudes usually have larger bodies and smaller appendages than their closest relatives in the tropics. Many animals have developed behaviors to help them overcome the cold: breeding, calving, burying and resting in the cavities are good defenses. And some animals undergo physiological changes as winter approaches: they accumulate fat reserves, develop a thicker fur and trap an insulating layer of air against the skin, under the fur or under the skin. feathers.

Nature has come up with other tips to help various animals deal with conditions that are impossible to bear, for example.

An animal standing in cold water or on ice benefits from a countercurrent heat exchange (1). The hot arterial blood (2) flowing from the heart warms the colder venous blood (3) that goes to the heart.
Ekann, CC BY-SA

Have you ever wondered how geese can seem to stand comfortably on the ice or squirrels in the snow, barefoot? The secret lies in the proximity of the arteries and veins in their extremities, which creates a warming and cooling gradient. When the blood from the heart moves up to the toes, the heat from the artery transfers into the vein that carries the cold blood from the toes to the heart. This countercurrent heat exchange allows the core of the body to stay warm while limiting heat loss when the extremities are cold, but not so cold that tissue damage occurs. This effective system is used by many birds and terrestrial and aquatic mammals and even explains how oxygen exchange occurs in the fish gills.

Carp in a partially frozen pond are doing well.
Starkov Roma /

Speaking of fish, how do they freeze from inside in icy waters? Fortunately, the ice floats because the water is very dense, allowing the fish to swim freely at temperatures that do not exceed freezing below the solidified surface. In addition, fish may not have the cold detection receiver shared by other vertebrates. However, they have unique enzymes that allow physiological functions to stay at cooler temperatures. In the polar regions, fish even have special "antifreeze proteins" that bind to ice crystals in the blood to prevent large-scale crystallization.

Another secret weapon in mammals and birds during long periods of cold exposure is brown adipose tissue or "brown fat," rich in mitochondria. Even in people, these cell structures can release energy in the form of heat, generating heat without muscle contractions or the energy inefficiency associated with shivering, another means the body uses to warm it up. This non-shuddering heat output probably explains why Anchorage residents can happily wear shorts and t-shirts on a spring day of 40 degrees Fahrenheit.

Of course, migration can be an option – although it is expensive in terms of energy costs for wildlife and financially for people who want to get closer to the equator.

As a species, humans have the ability to acclimate to some degree – some of us more than others – but we are not particularly suited to the cold. Maybe that's why it's hard to look out the window on a cold day and not feel bad for a crouching squirrel as the winter wind whips its fur. We may never know if animals dread the winter – it is difficult to evaluate their subjective experience. However, wildlife has a whole series of strategies that improve its ability to resist the cold, making sure to live for another spring.