White Fur

Photo by Stan Tekiela

by Stan Tekiela
© NatureSmart

April 19, 2021

As winter loosens its grip on the northern states and it finally feels like spring, my mind turns to all the changes in nature. In particular, the animals in the northern climates that change the color of their coats (pelage) or the birds that change their feathers (plumage) from brown to white and back again to brown in the spring.

Most people are familiar with critters such as Snowshoe Hares that change color for winter, but did you know that over 20 different kinds of animals and birds make this biannual change of color. And all of them occur in the northern hemisphere.

From early times there was a hot debate about how the change of color occurred. In the 1800’s it was believed that animals such as Snowshoe Hares grew longer white hair that covered up their brown hair. So basically, it was believed that they grew a new coat, but it was over the top of the old coat.

Others believed that the animals existing hair changed color or somehow bleached by the sun to a white color, thus NOT growing new fur. Or others argued that the hair follicle became damaged, and the hair died, and as a result it turned white just in time for winter.

Fast forward to current times and we now know that the fur is replaced in a process called molting, and new white fur replaces the brown. It has always been believed that the reason behind these seasonal changes was to blend into the environment. For example, for an Artic Fox to blend into the environment and allow them to get closer to prey. Or for Snowshoe Hare to blend in and not be seen. More than likely this is a great advantage when in a snowy environment. But a second reason has emerged for the season coat change. It not only helps them blend in, but a higher benefit is for added warmth.

Brown hair or feathers are filled with pigments called melanin. This is what gives the hair or feather its many colors and also provides structural support. However, the white fur or feather lacks the melanin and therefore are hollow. When sunlight enters the hair or feather, the light is scattered or bounces all around and what we see reflected back to our eyes is white. So, the space is causing the white color and also the space provides an air chamber that increases the insulating capacity of the fur or feathers by upwards of 27 percent. Close examination of the individual white hairs shows that the white hairs are wider than hairs with coloring, which allows more air space and thus greater insulating property. In addition, these hollow white hairs where narrower at the base and wider at the top allowing more hairs to be packed together near the skin surface, again increasing the insulation. 

 So, the next most logical question is, what triggers the seasonal change. Once again, the debate has raged for centuries. Historically there wasn’t much offered for an explanation, just that the weather was changing or that snow was on the ground. However, since the weather is never consistent from year to year and some winters having less snow than others it was never a good explanation. We now know that it’s the photoperiod, or the amount of daylight from sunrise to sunset that triggers the seasonal changes. If you think about it, it makes perfect sense. The amount of daylight is very predictable and doesn’t change from year to year. Special sensors in the back of the eye perceive the amount of daylight and sends signals the brain to direct what and when to grow the fur or feathers. 

We also now know that in addition to the white fur or feathers that are produced for winter, the critter also grows more fur or feathers than they have in summer. For example, birds will put on up to one third more feathers on during winter and mammals upwards of twice as many hairs.

There is much to consider and ponder as the days get longer and the snow melts away. There are many things changing in nature, including the animals. Until next time…

Stan Tekiela is an author / naturalist and wildlife photographer who travels the U.S. to study and photograph wildlife. He can be followed on www.facebook.com, Instagram.com and twitter.com. He can be contacted via his web page at www.naturesmart.com.