The Shape of Wildlife in Winter

Short-tailed weasels, also known in winter as ermine, have a long, slender body shape that allows them to invade subnivean tunnels to prey upon smaller mammals.
Photographer: Steven Hint
Courtesy Wikimedia
Licensed under Cc-by-sa-3.0

Hi, this is Mark Larese-Casanova from the Utah Master Naturalist Program at Utah State University Extension.

Now that snow is finally accumulating in Utah’s mountains, weekend hiking trips have come to an end. But, that means it’s time to dust off the snowshoes and skis and get back outside. We humans are lucky in that we have countless types of gear to help us adapt to almost all winter conditions.

While a fur coat might help keep mammals warm or camouflaged in winter, there are many other adaptations that also aid in winter survival. Decreased mobility in deep snow can often prevent animals from finding food, possibly causing starvation in winter.

Some animals have feet that are particularly large for their body size, which helps them travel on top of deep snow. One of the best examples of this adaptation can be found in snowshoe hares. Snowshoe hare prints are easy to spot among the spruce and fir trees- the large teardrop-shaped hind feet leave prints that look like the hare was wearing miniature snowshoes, which is how it got its name.

While some animals are adapted to walk on top of deep snow, others do their best to simply walk though it. The long, slender legs of moose help keep the majority of their bodies above the snow, minimizing the energy required to travel in winter.

Instead of walking on top of or through the snow, small mammals such as mice and voles travel under the snow. As snow accumulates, mice and voles create vast networks of tunnels on top of the ground, but under the snow. This subnivean environment is typically warmer than air temperature above the snow, and still provides access to food, such as grasses, seeds, and bark.

Short-tailed weasels, also known in winter as ermine, have a long, slender body shape that allows them to invade subnivean tunnels to prey upon smaller mammals. As long as its head can fit into a tunnel, its narrower body can follow. This adaptation comes with a price, though. Slender bodies lose heat quickly, so weasels must consume around one-third of their body weight in food each day in order to produce enough heat to survive.

So while deep powder might seem like a winter wonderland to those of us who can adapt with the right gear, other mammals continually struggle to stay warm and find food. Some, however, choose to give up the fight and sleep the winter away.

For Wild About Utah, I’m Mark Larese-Casanova.

Credits:

Images: Pending rights approval
Text:     Mark Larese-Casanova, Utah Master Naturalist Program at Utah State University Extension.
Additional Reading:

Ellsworth, E. Surviving the winter: The importance of snowshoe hare foraging behavior. BEHAVE: Stories of Applied Animal Behavior. University of Idaho. Available at: http://www.cnr.uidaho.edu/range556/appl_behave/projects/hare_forage.html

Gellhorn, J. (2002). Song of the alpine: The Rocky Mountain tundra through the seasons. Johnson Books.

Lieberg, A. (2009). Charismatic minifauna. Northwest Connections. Available at: http://www.northwestconnections.org/documents/news/EOE_09feb26_Lieberg.pdf

A New Winter Coat

Snowshoe Hare Summer Coat
Lepus americanus
Photo Courtesy US NPS


Snowshoe Hare Winter Coat
Photo Courtesy USDA Forest Service

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.

Credits:

Images: Courtesy US NPS & USDA Forest Service
Text:     Mark Larese-Casanova, Utah Master Naturalist Program at Utah State University Extension.
Additional Reading:

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 http://www.sciencedaily.com/releases/2009/02/090224220347.htm

Rust, C.C., R. M. Shackelford, and R.K. Meyer (1965). Control of Pelage Cycles in the Mink. Journal of Mammalogy, Vol. 46, No. 4 (Nov., 1965), pp. 549-565, http://www.ncbi.nlm.nih.gov/pubmed/5838224

Fraley, J. (2006). Snowshoe Hare: Lepus americanus. Montana Outdoors Portrait. Montana Fish, Wildlife, and Parks, http://fwp.mt.gov/mtoutdoors/HTML/articles/portraits/snowshoe.htm