Signs of Winter 5: Snowshoe Hares and Road Salt

Winter morph. Photo by D.G.E. Robertson. Wikipedia Commons

The North American distribution of the snowshoe hare (Lepus americanus) covers an extensive swath over the upper half of the continent. Most of Alaska and most of the provinces of Canada all the way east to Newfoundland and Nova Scotia are included in the snowshoe hare’s range. It is a species of the North! There are also, though, three finger-shaped, southerly extensions of the snowshoe hares’ range that follow the high altitudes of mountain ranges into remarkably low latitudes. In the far west, one extension runs down the Cascades and Sierras, and in the near west another follows the Rockies. The third extension, in the east, follows the scattered clusters of mountains that make up the Appalachians. The eastern subspecies of the snowshoe hare (L. americanus virginianus) is found in this Appalachian portion of its range, and these are the snowshoe hares we find in Pennsylvania.

Snowshoe hares live a wide variety of habitats, but they are especially abundant in forests that have a well developed shrub and underbrush layers. These hares are nocturnal or sometimes crepuscular and spend the daylight hours in shallow excavations under the cover of shrubs, ferns, downed trees or piles of branches. These daylight hideouts are called “forms.”

Snowshoe hares are well adapted to winter activity. They have very large back feet (from which their common name is derived) that enable them to move about easily over a snow cover, and they seasonally shed their fur to generate a white, winter camouflaging coat. They eat a wide variety of plant materials and seasonally consume whatever food stuffs are available. They are even known to eat dead mice and other small animals (and even meat from baited traps) to add protein to their relatively poor quality diet. Green, leafy vegetation is their predominant food in spring and summer, while bark, buds, twigs and evergreen needles are their primary foods in the winter. These hares are in turn eaten by a wide variety of avian and mammalian predators.

Summer morph. Photo by W. Sigmund, Wikipedia Commons

The southerly distribution of the snowshoe hare in Pennsylvania coupled with their very specific adaptations to cold, snowy habitats make them very interesting organisms for studying the early impacts of climate change and global warming. Researchers at Penn State have been monitoring Pennsylvania snowshoe hares for the past several years and have seen some interesting trends in their morphology, behavior and physiology.

For example, Pennsylvania snowshoe hares are now larger than snowshoe hares living in the Canadian Yukon, and their fur is shorter and less dense. A shorter, food-limiting winter season in Pennsylvania could explain the size differences and the reduced coat might reflect less extreme winter temperatures. A less well insulated animal would function more optimally in a warmer winter. Further, Pennsylvania snowshoe hares are exhibiting a much less obvious winter color change. Fewer of the PA hares are turning completely white, and a number are retaining their summer-brown coats throughout the winter. The reduction in snowfall throughout Pennsylvania may be setting up a classic natural selection system in which the white rabbits stand out more clearly against the predominantly brown landscape and are, thus, being preferentially taken by predators.

Pennsylvania snowshoe hares also produce less metabolic heat in the winter compared to their Yukon counterparts and select their winter resting spots for their potential cover and protection from predators rather than for their optimal thermal advantages. Subtle, yet very logical and very adaptive changes, then, are being observed in this winter-focused species!

Photo by T. Brueckner, Flickr

Far away from the mountain habitats of the snowshoe hares humans are mining and spreading rock salt (halite) so that their roads and sidewalks are useable throughout the icy winter. Most of the rock salt spread on roadways in Pennsylvania comes from deep mines in nearby Ohio where massive deposits of halite were laid down by the evaporation of a shallow, tropical ocean some 400 million years ago. The United States spreads between 17 and 20 million tons of rock salt on its roads each winter. This salt unquestionably makes driving (and walking!) safer, but it also causes considerable damage to cars, concrete, asphalt, plants and lawns. Salt spread on roadways and sidewalks also moves out into the surrounding ecosystems and may lead to some very distant and very unexpected problems.  Two of Barry Commoner’s Four Laws of Ecology apply here: “Everything is connected to everything else,” and “Everything must go somewhere.”

Photo by K. Emigh, Penn State Sites

Penn State Erie (The Behrend College) is an excellent place to look at ice and snow (and salt). Typically Erie, Pennsylvania gets 113 inches (almost 10 feet!) of snow a year, and last month (December 2017), Erie set a record with a monthly total of 63 inches of snow! Penn State Erie spreads more than 500 tons of rock salt on its sidewalks and parking lots each winter and PennDOT (the Pennsylvania Department of Transportation) adds another 27,500 tons of salt to the streets and highways of the surrounding Erie County. Dr. Pam Silver, a distinguished professor of biology at Penn State Erie, applied Commoner’s two laws and wanted to find out where all of this spread salt ends up. So, several years ago, she and some of her students began to test the snow around campus and the waters of the nearby wetlands and streams to see if they could monitor the movement and ,possibly, the impact of all of this salt.

Some constructed wetlands near a road built on one side of the campus offered an excellent experimental design for part of this study. The water in these wetlands was new and unexposed when they were established three years ago. One of these wetlands, though, directly received flow from the new road (which was salted in the winter) while the other was isolated from the road runoff. Yearly monitoring of these wetlands showed clearly that the roadside wetland had significantly elevated salt concentrations and that the invertebrates in its sediment were greatly reduced. These invertebrates serve as part of the base of the food web of the entire aquatic ecosystem that extends on into nearby Lake Erie. Salt induced declines in these invertebrates may foreshadow subsequent declines in the fish and amphibians that rely on these invertebrates for food.

At several sampling points around the campus salt concentrations were detected that exceeded safe salt levels for human drinking water. The potential impact of this salt as it inevitably moves into Lake Erie (from which drinking water is obtained) must be considered in terms of human health consequences and also in terms of the cost for effective water treatment.

Everything is connected to everything else. Everything must go somewhere. Snowshoe hares in Pennsylvania are changing because atmospheric carbon dioxide levels are increasing. Rock salt spread on Pennsylvania sidewalks and roadways may be killing off fish in our streams and lakes! Everything is connected! What an important lesson for us all.

 

 

 

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2 Responses to Signs of Winter 5: Snowshoe Hares and Road Salt

  1. ron says:

    Wonderful stuff.

  2. Jesse H Bruton says:

    A lesson I wonder if humanity will learn in time to save us all.

    Thanks for this site and the wonderful writings… you have a new fan!

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