(This column was first published in the January 14, 2002 Buffalo News.)
Last week I wrote about the activity of insects and
mammals under the snowpack in tiny caves called pukak. But not all animals --
and in particular not larger ones -- have access to those caverns.
The rest, humans included, have to make our way
cross-country at this time of year as well as possible -- hopefully over the
snow but more often through it. We urbanites and suburbanites don't often think
about this because we enjoy the benefits of automobile transportation and even
when we walk, snowplows create pathways for us. Wild animals don't share these
benefits, nor do we if we hike across open fields or through trackless woods.
As I write, the snowpack in my yard has generally
reduced through evaporation, sublimation and melting to a depth of about a
foot, but rewind the calendar to December 28th and recall how that 82 inch
snowfall left us with 44 inches on the ground. (The Lewis County town of
Montague in the Tug Hill Country east of Lake Ontario had still more: 127
inches of snow that produced a snow depth of over six feet.) Consider the
problems faced by different species crossing such fields.
Winter-active arthropods like stoneflies, crane flies
and springtails face none at all. They are light enough to walk on the surface
of the snow. So too are a few small mammals like mice and, when the snow has
settled enough to give it a little more firmness, chipmunks, red squirrels and
weasels can also make their way.
The quality of the snow makes an important difference.
Many of us recall walking on crusted snow that, at least when we were children,
bore our weight. Occasionally we broke through and had to pull up our leg to
move on, many times breaking the crust under the other foot in the process. The
early soft snow – especially lake effect snow -- offers no such support.
It is light as foam. I recall the first time I tried a new pair of snowshoes in
such snow. They offered no support at all and I might as well have left them
home. But over time snow thickens and provides something between those two
extremes.
What is it that allows some animals to progress better
through snow? The answer derives from simple physics. Two factors come into
play: weight and the surface area pushing down. Small animals are lightweights
and their legs are so short that their entire bodies "float" on the
surface. They can effectively swim over the snow.
Not so larger animals. Clearly, light weight and big
feet serve best, thus the outsize feet of animals like snowshoe hares, lynx,
mountain lions and wolves. Deer, on the other hand, are terribly served in this
regard. Their tiny hooves (and to some extent their lower legs) break through
even crusted snow. And, recalling that lovely sequence from the movie
"Bambi", even ice gives them problems.
Coyotes and wolves, for example, enjoy a big advantage
over deer. (In pounds per square inch, the canines' 1.8 is a vast improvement
over the deer's 6.3.)
Remarkably, and even though our weight is carried on
two rather than four, our still bigger feet make us equal to these wild dogs.
And we can do still better with snowshoes. A mid-sized pair reduces that
pressure to less than a half-pound per square inch. This gives us a tremendous
advantage over all other medium or large-sized North American animals. We can
quite literally walk on snow.
Of course, most wild animals overcome their
disadvantage through additional strength, agility and condition.