White creatures changing with the season

Author: 
Ned Rozell
Article Number: 
2,304
April 14, 2016

This morning, through the west window, I noticed a flash of white. I looked up from breakfast to see a short-tailed weasel popping from a hole in the snowpack. He was sleek and streamlined and snow-white, except for where his tail looked like he dipped it in black paint.

Later, a leggy snowshoe hare bounded away, and then paused nervously. Those sightings inspired a visit to my neighbor, who could tell me more about their white coats, the ones that won’t be white much longer.

My neighbor, who may be hosting the weasel at this moment (their home range can be as expansive as 40 acres), is Dave Klein, who has been curious about Alaska animals great and small since before he first drove up the Alaska Highway in the 1940s.

Klein, a professor emeritus at the University of Alaska Fairbanks, said that both weasels and hares undergo a molt that changes them from winter white to summer brown. That means they will soon replace their white fur with brown fur, presumably to remained camouflaged for the change of seasons.

Triggering this color change is hours of daylight, “but over long periods of time, (the fur-color change) is related to changes in timing of the melting of snow,” Klein said.

If warmer spring temperatures start melting snow earlier, for example, hares and weasels would be able to adapt and remain inconspicuous, “but that might take several generations,” Klein said.

Early adapters to a changing climate would pass on their genes. Late adapters might become lunch for great horned owls. Or, in the case of weasels, they might get no lunch at all.

Klein also offered up an observation of an animal that does not change fur color with the season. Arctic hares (larger than snowshoe hares and not confined to forests, often living on open tundra) in the high arctic of Canada and in Greenland stay white all year round. Replacing white fur with brown during the brief summer might be too costly energy-wise for those far-north hares.

“You can spot them from miles away in summer,” Dave said.

Arctic foxes also show some fur-color variation, depending on where they live. In the Aleutians and Pribilof Islands, most arctic foxes don’t turn white, instead morphing to a “blue” phase.

As you move farther north, arctic foxes have differing degrees of whiteness in winter. For example, while only a few foxes turn white on the Pribilof Islands, most of them living on St. Lawrence Island turn the color of snow.

Arctic foxes on the North Slope always change to white, which Klein thinks might be important so “they can sneak up on polar bears on the adjacent sea ice and grab a snack,” from a seal kill. Red foxes might not be able to get as close to a polar bear (which stay white all year, perhaps because they spend so much time on sea ice).

Brown lemmings, abundant in places like Barrow, don’t change the shade of their fur, but collared lemmings do, perhaps because they leave the subnivean world under the snow more often than brown lemmings. The whiteness of collared lemmings gives them a chance of remaining undetected by other hungry creatures wearing similar winter camo — snowy owls and arctic foxes.

Since the late 1970s, the University of Alaska Fairbanks' Geophysical Institute has provided this column free in cooperation with the UAF research community. Ned Rozell is a science writer for the Geophysical Institute. A version of this column appeared in 2009.