Fat, Fur, and Feathers: How Animals Survive Winter (Polar Vortex or Not)

December 16, 2016 | Maggie Romuld

arctic hare
Photo credit: skeeze/Pixabay

Everyone’s talking about the Polar Vortex this week, and it’s hard not to feel sorry for the wildlife outside our windows. But should we?

While we can only wait out the current blast of Arctic air with hot chocolate and old Christmas movies, most animals in cold climates are highly adapted to survive extreme weather. How do they cope with the cold? They use a variety of mechanisms. Some are extremely complex chemical strategies, such as supercooling, but some are comparatively simple—fur, fat, and feathers designed to keep in the heat.

Air is an excellent insulator, and birds survive in sub-zero weather by fluffing their feathers to introduce air and create layers of air and feathers. Moreover, long before we discovered down as the perfect material for ski coats and comforters, birds used small, fluffy, down feathers as insulation against the cold. According to the Audubon Society, “Just a fraction of an inch of this insulation can keep a bird’s body temperature at 104 degrees Fahrenheit (40 degrees Celsius), even in freezing weather.”

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Fur also traps air next to an animal’s body, and lots of animals add insulation by changing their coats with the seasons. Some grow an additional wooly underfur that they shed in the spring, while others simply grow a denser, thicker winter coat.

Some animals—including Arctic foxes, ptarmigan, snowshoe hares, and weasels—completely change their fur (or feathers) to white winter wear, partly as camouflage against predators, but also for insulation. According to a report from North Idaho, a snowshoe hare’s winter coat is 27 percent more insulating than its summer coat, in part to the density of the hairs, but also the color. “Brown hair is filled with pigments to make the brown color. White hairs lack these pigments, giving them the white color, and nothing replaces the pigment except air. The air trapped within the hair provides additional insulation on top of the air trapped between the hairs.”

The hair structure of ungulates, such as deer and moose, also changes from solid to hollow shaft when they molt for the winter. Polar bears have hollow-shafted hair year-round, but unlike deer, polar bear hair is transparent, and the hollow core scatters and reflects visible light.

Fat doesn’t transfer heat as well as muscle or skin. Marine mammals that have evolved to live in cold waters, such as whales, seals, sea lions and polar bears, have adapted to conditions by relying on a thick layer of body fat (blubber) beneath the skin to provide insulation against ice cold water.

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Other animals work hard to build up fat reserves, less for insulation and more as a way to subsist through periods when food is scarce or has little energy value. Some animals go into short-term sleep (torpor) when their body temperature drops and their heart rate and metabolism slow; others go into longer-term sleep (hibernation).

Gaining weight and sleeping? Sounds like a perfect way to wait out the winter.

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