May 4, 2013, by Tim Radford
Camouflage does work: A snowshoe hare in Canada
Image: Ansgar Walk
FOR IMMEDIATE RELEASE Species which protect themselves by turning white to match the snow of the long northern winters may be caught out as a warming climate reduces the numbers of days of snow cover. LONDON, 4 May – Milder winters mean bad news for the snowshoe hare of western North America. Lepus americanus is famous for two things: an evolutionary camouflage adaptation that keeps it white in the winter snow and turns it a reddish brown in spring and summer; and its intimate population polka with one of the continent’s most glamorous predators, the Canada lynx. When hares are numerous, the lynx population increases. As the numbers of hares diminish, so its predators go hungry and the lynx population starts to drop, giving the snowshoe hares another chance. But the hare may be losing the battle, thanks to climate change. Biologists report in the Proceedings of the National Academy of Sciences that they monitored 148 wild hares in western Montana and observed that the adaptation that gave the hares an advantage in stable climates is likely to work to their disadvantage as temperatures rise, snow cover shrinks and the winters get shorter. The three years of their study included both the shortest and the longest snow seasons since 1970. The researchers found that the spring and autumn moults seemed to occur independently of the arrival of the snows: they conjecture that they may be triggered by changes in daylight length. Since hares don’t get much chance to die of old age – predation comprises 85 to 100% of mortality in different regions and different years – camouflage would play an important role in keeping hares alive long enough to breed and rear their young.
A white hare on brown soil or a brown hare in the snow would both be at a serious disadvantage. Over the three-year period, the researchers had plenty of chances to observe both. They expect “increased coat colour mismatch as snow seasons shorten under future climate change” and without rapid adaptation, this mismatch will increase as much as fourfold by mid-century and eightfold by the late century if humans go on pumping greenhouse gases into the atmosphere at an increasing rate. The average annual duration of snow cover is forecast to fall by 29 to 35 days by mid-century and by 40 to 69 days by the end of the century. Hares, the researchers warn, won’t be the only coat-changing mammals left exposed by ever-shorter winters. They conclude that there is a lot to learn from the plight of the hare (and see our story of 18 January).. “The compelling image of a white animal on a brown snowless background can be a poster child for both educational outreach and for profound scientific inquiry into fitness consequences, mechanisms of seasonal coat colour change, and the potential for rapid local adaptation”, they say. – Climate News Network
Tim Radford, a founding editor of Climate News Network, worked for The Guardian for 32 years, for most of that time as science editor. He has been covering climate change since 1988.