The forest-dwelling snowshoe hare (Lepus americanus) has the remarkable ability to change the color of its fur from brown in summer to white in winter in order to camouflage itself. However, as a new study in the journal Ecology Letters reveals, human activity is causing a snowfall reduction, leaving the wintry white hares standing out to predators like light bulbs, and increasing their mortality rate.
A recent study has suggested that two-thirds of all recent dangerous climatic events are directly attributable to human-produced (anthropogenic) greenhouse gas emissions. These impacts include the rapid alteration of ecosystems, including the types of forests inhabited by the snowshoe hare.
As the new study outlines, the snowshoe hare is remarkably well adapted to its North American environment. It is herbivorous in summer, but when resources are scarce in the winter, it is known to opportunistically become carnivorous to satiate its hunger. A nocturnal animal, it has specialized feet that prevent it from sinking into the winter snow and that protect it from very low temperatures.
A major predator of the hare is the lynx, a fast hunter over twice the size of the average domestic cat. Fortunately, the snowshoe hare has a clever defense mechanism: It is able to change its fur to white to match the color of the snowfall in winter, and brown to match the earthy ground in summer. These changes take about 10 weeks to completely occur, and are related to the production of melanin, a pigment, in its body. The more melanin in the fur, the darker it will be.
The summer morph of the snowshoe hair. Walter Siegmund/Wikimedia Commons; CC BY-SA 3.0
The rabbits detect the changes in the seasonal light through specialized retina cells, which let the brain know when to alter the production of melanin to match the fur coat color to the season. However, previous research has recognized that a decrease in snow due to increasing global temperatures has caused a mismatch between when the white fur appears and the start of a snowy winter.
In order to investigate if this causes an increase in mortality rate, the researchers of this new study tagged 186 snowshoe hares with radio collars in two large swaths of hare territory in Western Montana. These hares were monitored once a week for several years, particularly during the seasonal transitions from summer to winter.
As the light levels remained the same as global temperatures rose, the hares do indeed change their fur color too early for the increasingly delayed snowfall; consequently, as the radio collars showed, their survival rate has been dropping for some time. In fact, their weekly survival rate suffers a 7 percent drop when snow arrives late or leaves too early.
“This paper shows that the mismatch costs are severe enough to cause hare populations to steeply decline in the future unless they can adapt to the change,” said Marketa Zimova, lead author of the study, in a statement.
Only time will tell whether or not individuals are able to change their fur color at slightly different times to adapt to the changing snow, and if they can survive long enough to pass on this ability to their offspring. Either way, the evolutionary clock for the snowshoe hare is ticking.
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