Nature Notes – From the Backyard to the Biosphere. How the Wild Things Stay Warm

It was hailing today. First the rain was coming down. Then, as the temperature dropped, the rain turned to hail, and the bone-chilling cold started to set in, I began to think about how hard it must be to be a wild thing during our frigid winters. How on earth can so many species make it through the long, cold season? Many wild animals migrate to warmer climes when the going gets tough, but many others must begin at this time of year to pull out of their evolutionary tickle trunks the tricks they use to cope with the harsh, cold climate we share.

From geese to toads, and from turtles to foxes–the wildlife we know and love has a dazzling array of adaptations to deal with what we try our darndest to avoid: the cold. How can an Arctic fox look so cheery and care-free as it trots along through the snow on a -300C day? How can a duck casually pop into the frigid lake, just feet from a sheet of ice? How can a salamander, with skin so delicate that human handling can cause serious damage manage to it, survive the long winter months?

The first thing to know about staying warm is that the concept has a name: thermoregulation. While there are a couple of different ways of classifying animals according to how they maintain their body temperature, animals fall into essentially one of two groupings: endotherms vs. ectotherms.

Endotherms are the birds and mammals: the animals that maintain their body temperature, well, let’s say internally. Ectotherms (all the other animals) rely on the external environment to regulate their temperature. Ever see a really tired-looking fly by the window in December? If it isn’t buzzing around incessantly, doing its bug thing, then the animal is probably too cold; this ectotherm likely doesn’t have enough externally-derived heat to get its body going. How about the turtle, sunning itself on the log? It isn’t just a beach bum: turtles, like all ectotherms, actually need the sun’s warmth to fuel their activities.

So what do ectotherms do, then, to survive the cold winter months? Turtles, resourceful critters that they are, burrow into the mud and enter a state similar to what we know as hibernation. All of the bodily processes slow way down, and in the pretty much thermally-stable below-ground environment, the turtle is able to squeak by and survive the winter. Hibernation-like behaviour in thermally-protected places is really the only way that ectotherms can survive the cold.

However, another ectotherm adaptation has little to do with survival of the current generation. Some species of insects, for example, will lay their eggs in the fall. The adults’ life may well come to an end at that stage, but their offspring are able to carry on. Hidden well under leaf matter, bark, or some other protective shelter, the undeveloped young can wait out the winter, only starting up the metabolic engines when the conditions improve come spring.

For the most part, endotherms aren’t afforded such luxuries. A few species (e.g. the Black Bear and the Groundhog) do go into full hibernation in protected underground dens, only awakening when the sun begins to stick around for a little longer and food sources spring to life once again at the end of winter. But many animals remain fully active during the long, cold months.

Shelter does play an important part in the survival of many species of wildlife: cavities in dead trees; thick nests lined with leaves, fur and other insulating materials; and even simple depressions in the snow help birds and mammals to keep the cold out and the warmth in.

However, retreating to nests, dens and cavities is a behavioural response to the cold. Animals that remain in our part of the world for the winter also have many physiological ways of maintaining their body temperature. Growing a fur coat so thick that physical exertion can actually lead to overheating is the compensation mechanism of choice for animals like the Arctic fox. With layers of hairs that act to trap air and keep it still (thus becoming one of the best insulators around), the typical mammalian response of growing a specialized winter coat transforms what could seem an animal’s worst enemy (the air around it) into its best friend.

The feather structure of birds acts in a similar way, trapping air between layers of perfectly-aligned overlapping barbules (individual hair-like elements of a feather). Constant preening (running the beak along the length of the feather) ensures that any misalignment is instantly repaired–thus getting rid of any pathways through which air could begin circulating. Preening is thus a critical winter activity. Preening also serves to continually spread a bird’s natural oils throughout the feather structure to repel water. Essential for aquatic birds in particular, all endotherms must take advantage of their natural oils to keep frigid, heat-stealing water at bay.

One of the other main mechanisms wild animals use to stay warm is something we all love to hate: fat. While we humans may have a particular phobia of this very practical substance, fat is in, for much of the animal world. In fact, for the whales and seals that playfully loll in arctic waters, fat is phat: these animals’ survival very literally depends on just how much tubba they can pack on. With incredibly-efficient insulating properties, layers of body fat help to ensure that the core temperature of these animals remains constant, despite their very frigid external environments.

So fur and feather, mud and fat, holes in the ground and air in a trap: these are the tricks of our wild friends. Winter can be a tough time for many creatures, but the adaptations with which evolution has furnished the wild things sure help to make the coming season a little easier to deal with.

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