White snowshoe hare in Montana (Photo: L Scott Mills)

Species go extinct unless they can adapt to changes to their environment. And while the climate change caused by humans is often viewed as a future threat to wildlife, it's already having a measurable impact on species today.

One potential casualty of climate change is the snowshoe hare. A close relative of rabbits, the hare's hind feet (its 'snowshoes') have a large surface area to stop it sinking into snow. It also has another adaptation for life in North America: the animal's brown summer coat turns white in winter, providing camouflage to hide it from predators.

While some species are suffering from direct effects of global warming, such as higher temperatures or drought, others are facing indirect challenges from not matching their environment. The latter is literally true for snowshoe hares: as climate change reduces the duration of snow cover, an animal whose white fur doesn't molt in time will stand-out like a lightbulb against the darker background, making them easier to hunt.

The survival cost of camouflage mismatch has now been measured in a study led by L Scott Mills of North Carolina State University, published in the journal Ecology Letters. Mills and his student Marketa Zimova used radio-tagged collars to track snowshoe hares in western Montana every week over 2-3 years. They found that animals with mismatched coat color had a 7% lower survival rate.

"This is one of the most direct demonstrations of mortality costs for a wild species facing climate change," Mills said in a press release. And while snowshoe hares aren't currently endangered, the biologists predict that the higher death rate will lead to a significant drop in population levels by the end of the century.

But the chances of extinction can be minimized by a conservation strategy called 'evolutionary rescue': if a population is made-up of a large variety of individuals, it will have a deep gene pool, maximizing the likelihood that at least some individuals carry a genetic variant that would help them to survive and reproduce. This would enable a population to adapt through natural selection. For hares, this means individuals with genes that make them molt at times which match snow cover (it's unknown whether they would be able to adapt in time).

Evolutionary rescue could potentially be used to save many animals from climate change, including at least 14 species that change color, such as white-tailed jackrabbits, weasels and arctic foxes.
