Stopping by the Woods on a Snowy Afternoon

The quiet of a forest on a snowy February afternoon is something special:

You would almost imagine that the whole forest was uninhabited. And yet, you can still find things like this:

This short little street was created by these guys:

Fox Squirrel, (Sciurus niger), Colorado Springs, CO, 12/28/2011

And this trail, leading off into the brush?

By this guy:

White-tailed Deer, (Odocoileus virginianus), Illinois Beach SP,
Lake Co, IL, 7/8/2012

Deep snow actually has some significant implications for deer. Unlike squirrels, they can't easily stay on top of it, with all of that weight over some pretty small feet. Unlike woodchucks and chipmunks, they're too big to simply hibernate. So really deep snow causes them to expend a lot of energy just to move around, which they have to do in order to keep eating. They actually handle it by finding an area within some sort of cover and staying there, which means that as they move they tromp the snow down, creating a sort of "yard" that they can move around in with a minimum of effort.

Here in Illinois, a severe winter like this one will mean fewer deer next spring, despite their yards. In places like northeast Minnesota, a severe winter can have major impacts on the deer population the following year. (1) As the world warms, though, severe winters are on the decline. Which, of course, means deer populations are likely increasing.

Moose, (Alces alces), Anchorage, AK  8/12/2012

 

What's good for deer, though, may not be good for their neighbors. Moose in northeastern Minnesota are already near the southern edge of their habitable zone, to the extent that warmer summers are likely to cause them to disappear from the area. (2) And the increase in deer may accelerate that trend -- deer in Minnesota are known to carry Pneumostrongylus tenuis, a nematode that goes by the nickname "brainworm". (3) It doesn't often harm deer except under stress, but Moose were apparently only exposed to them as late as the mid-20th century, as deer populations expanded north. They do not handle the worm well, and this has apparently contributed significantly to decreases in Moose in NE Minnesota. (4) Shorter, warmer winters means higher deer winter survival, which means more opportunities for Moose to be infected, which means fewer Moose. And so White-tailed Deer end up as climate change's executioners.

That quiet, peaceful forest scene belies the difficulty of the winter season for those creatures that don't have snug, warm houses to escape to, but paradoxically, an easing of that winter may well spell trouble for many critters.

(1) Post, E., & Stenseth, N. C. (1998). Large‐scale climatic fluctuation and population dynamics of moose and white‐tailed deer. Journal of animal ecology, 67(4), 537-543.

 

(2) Lenarz, M. S., Fieberg, J., Schrage, M. W., & Edwards, A. J. (2010). Living on the edge: viability of moose in northeastern Minnesota. The Journal of Wildlife Management, 74(5), 1013-1023.

(3) Karns, P. D. (1967). Pneumostrongylus tenuis in deer in Minnesota and implications for moose. The Journal of Wildlife Management, 299-303.

(4) Murray, D. L., Cox, E. W., Ballard, W. B., Whitlaw, H. A., Lenarz, M. S., Custer, T. W., Barnett, T. and Fuller, T. K. (2006), Pathogens, Nutritional Deficiency, and Climate Influences on a Declining Moose Population. Wildlife Monographs, 166: 1–30. Doi: 10.2193/0084-0173(2006)166[1:PNDACI]2.0.CO;2