Hi, this is Mark Larese-Casanova from the Utah Master Naturalist Program at Utah State University Extension.
November is the time of year in Utah when the weather takes a quick turn from autumn to winter. As the line of snow from occasional October storms creeps further down the mountains, I’m inspired to bring wool sweaters and down jackets out of storage. It’s easy for us to simply wear extra layers, but what about the animals that live high in the mountains, where winter set in weeks ago?
While some mammals are cued by their internal clocks to begin sleeping the winter away, many brave creatures prepare to spend the winter searching for food. Being active in the cold requires a warmer coat, just like it does for us. The reduced amount of daylight in autumn triggers hormones that cue many mammals to grow a thicker and warmer fur coat.
Some mammals, such as weasels and hares, counter the onset of winter by ‘changing’ the color of their fur from brown to white. For instance, snowshoe hares grow long, white guard hairs that cover their brown fur in winter. The snowshoe hare benefits from this thicker, white fur not only by retaining heat, but also by using camouflage to hide from its many predators.
Surprisingly, white fur also helps insulate. It might make more sense for brown fur to be warmer since it is darker in color. But, white hairs, which lack the pigment melanin, have more air spaces that result in greater insulation.
While weasels are predators, there are other animals, including birds of prey, that feed upon them. The winter coat of the ermine, also referred to as the short-tailed weasel, is entirely white, except for the black tip of its tail. When an ermine runs, the tip of its tail swings wildly, drawing the attention of a predator away from its body to its expendable tail.
The timing of change from brown to white fur in autumn is critical to survival. An early snow can create a white backdrop for a snowshoe hare that is still brown, likely increasing the chance of predation. Conversely, a lack of snow late in autumn can make a snowshoe hare that has already turned white stand out like a sore thumb.
The number of days with snow on the ground has been decreasing in mountainous areas, and predation of snowshoe hares has been highest in spring and autumn. In some areas of the country, such as the Cascades and Olympic Mountains, snowshoe hares are mottled white and brown year round, or never turn white in winter. Comparing these populations to others across the West will help us better understand how animals, such as the snowshoe hare, are able to adapt to our changing climate.
For Wild About Utah, I’m Mark Larese-Casanova.
Images: Courtesy US NPS & USDA Forest Service
Text: Mark Larese-Casanova, Utah Master Naturalist Program at Utah State University Extension.
University of Montana (2009, February 24). Climate Change Hurting Hares: White Snowshoe Hares Can’t Hide On Brown Earth. ScienceDaily. Retrieved November 22, 2011, from https://www.sciencedaily.com/releases/2009/02/090224220347.htm
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Fraley, J. (2006). Snowshoe Hare: Lepus americanus. Montana Outdoors Portrait. Montana Fish, Wildlife, and Parks, https://fwp.mt.gov/mtoutdoors/HTML/articles/portraits/snowshoe.htm