It happens every fall. Male birds change from vibrant mating plumage to duller winter colors. White-tailed deer turn from red-brown to brown-gray, and snowshoe hares turn from brown to white.

According to biologists at Arizona State University’s School of Life Sciences, the length of daylight triggers seasonal color changes in wildlife. With birds that raise their young during fair-weather months, as days get longer in spring, the males don their colorful mating feathers. Some also have color shifts in other body parts. For example, House Sparrows have black beaks when breeding and yellow beaks when they aren’t.

DID YOU KNOW?
The chameleon – the poster creature for rapid change color – has two layers of outer skin cells, called iridophore cells, that it adjusts by relaxing or tensing to reflect light in different ways, producing different hues. It’s a guy thing. Only mature male chameleons can dramatically shift their color on command.

Likewise, shorter days trigger a color change. In the fall, some animals in the weasel family – including ermine and long-tailed weasels – change from brown to white, which takes about a month. The color change starts on their stomachs and then spreads upward to help them blend into the snow. Only the tips of their tails remain black during the winter. It’s a genetic trait – northern species of weasels still become white in winter even if they are relocated to a southern climate.

White-Tailed Deer. For animals such as white-tailed deer that are subject to hot summers and cold winters, having two coats also helps control body temperature. According to the Maryland Department of Natural Resources, a deer’s gray winter coat has longer outer hairs, called guard hairs, and soft, dense underfur for insulation. They shed this double coat in the spring, replacing it with short, wiry hairs. Hormonal changes that occur with the changing seasons trigger this biannual molt.

Location can affect a deer’s fur color too. “Coat color, regardless of the season, tends to be darker in forested areas and lighter in agricultural areas where deer are exposed to more direct sunlight,” says Michelle Carstensen, wildlife health program supervisor for the Minnesota Department of Natural Resources.

Birds of a Feather. Most birds molt once each year, but some – such as Scarlet Tanagers – do it twice a year. Tanagers turn from dull green to bright red in the spring, then back to green again in the fall.

The most dramatic seasonal changes in a bird’s appearance are the result of molt – replacing old feathers with new, says birding expert David Sibley in BirdWatching magazine. “Growing a full new set of feathers takes a lot of energy .… Consequently, many species molt just once a year. But that doesn’t mean they look the same year-round; they can take advantage of other means of changing their appearance.”

IT'S A FACT
Fur, like human hair, is prone to sun damage, which is why animals shed. If they didn’t, they would look lighter and lighter over time.

Feathers are dead matter and subject to wear and tear by sunlight and abrasion, similar to human hair. Melanin, a black pigment, gives darker feathers and feather parts more resistance to wear, which gives birds an energy-efficient way to change color. For example, male Red-winged Blackbirds molt only once in late summer, when they grow black feathers with light-colored edges. Over the course of the winter, the pale edges of the feathers wear off. By spring, blackbirds appear fully black again.

Diet also affects coloration. Birds like Cedar Waxwings that eat lots of red berries turn redder in color. Other eye-catching hues, including yellow and orange, also come from pigments in food. (It happens to humans, too. If you eat a lot of carrots, your skin takes on an orange hue. So it’s true that you are what you eat!)