by Claire Polfus
It’s about that time. The leaves hug the forest floor rather than whisper to the wind in the canopy. The nights scatter a frosty pattern across my windows. The cool breeze tantalizes my toes with the anticipation of snowflakes and skis. And, it is dark. It is dark as I wait for the bus in the morning and as I make my way home in the evening. The days are getting shorter and the long nights of winter are starting.
Many of fall’s keystone changes are set off by the diminishing light. One of these is the changing fur of the snowshoe hare (Lepus americanus). Snowshoe hares look like large rabbits (although they are not all that closely related to the cottontails in our Champlain Valley backyards) with extra-large back feet, which they use to run on top of the snow in the winter and evade their predators. Their range extends from arctic tree-line through the extent of the North American boreal forest down to its southern reaches in the high elevations of Southern Appalachia and the Colorado Rockies. Everywhere you find snowshoe hares, you find snowy white winters. In order to camouflage themselves during the snowiest months, they molt from a dusky brown in the summer to a pure white in the winter.
In fall, the shrinking daylight prompts the hares to shed their outer layer of brown fur and regrow a new and more insulative white outer fur. The opposite occurs in the spring. While they are molting they are generally at higher risk for predation since they are both brown and white and can blend into neither snow nor ground. One of the most embarrassing sights you can see as you explore the woods in the fall is a white and brown hare frozen in place wishing and failing to be camouflaged against a backdrop of fallen leaves!
Thus far in the evolution of snowshoe hares, the advantages of camouflage in the winter have outweighed the heightened risk of predation in the spring and fall. Unfortunately for the hares, they evolved in a world where daylight and temperature aligned, at least on average, in a certain way. Since climate change is altering temperatures and precipitation but not day length, this alignment is becoming skewed. In Montana some researchers are finding that the period where the hare’s fur does not match its surroundings is lengthening. This is great for predators for the time being, but if hare populations become too deflated, the boom may become a bust for lynx, bobcat and great-horned owls.
Adaptation to changing seasons is necessary for every northern species. As I step out of my house in progressively warmer jackets, I know that the hares up in the mountains are becoming progressively whiter. Soon there will be snow and we will be racing each other across the mountain meadows – if I can find one first!