Snowshoe hares change their coat colour from pure white in winter to almost entirely brown in summer, save for their furry feet, which stay white all year round. They are one of only 11 animal species that use such a camouflage strategy – matching a background of snow in winter and the undergrowth in summer. It's a clever wardrobe change that has served them well in the stable climate of past centuries.
“It's a clever wardrobe change that has served the hares well in the stable climate of past centuries. But now that climate is changing.”
But now the climate is changing, meaning winter snow doesn't stick around for quite as long. For snowshoe hares, the result is a period of time when hair colour and the background environment are mismatched. The sharp contrast leaves them exposed to danger: they're more likely to be seen, captured and gobbled up by hungry lynx and many other carnivores, as research in Northern Montana led by Dr. L. Scott Mills and Marketa Zimova at North Carolina State (and previously University of Montana) has shown.
If the trend persists, the number of 'mismatched' days will grow by four- to eight-fold by the end of this century, leading researchers to wonder what the future holds for the species. Will it adapt, survive and thrive? Or will this new turn in the predator-prey game of hide-and-seek be too much to cope with?
Snowshoe hares occur across a wide swath of the US, from the Atlantic to the Pacific coast, stopping short just below the Arctic Ocean (where their Arctic cousins live). This fascinating colour-shifting species has been studied for centuries (as far back as 1784), and scientists have been particularly fascinated by its wildly fluctuating boom-bust ten-year population cycles in the northern part of its range. In contrast, few have investigated hare coat colour change, with most studies focusing on small geographic areas. Mills, along with researchers Skyler Suhrer (University of Montana) and Beau Larkin (MPG Ranch), wanted to find out how (and if) the timing of the colour moults and mismatches varies depending on where a hare lives.
The team contacted parks and other places where remote camera traps had been installed (often for the study of larger species like bears and lynx) and asked for 'bycatch' photos of hares taken at these sites. A clever and non-invasive way of observing animals in the wild, camera traps are attached to fixed locations (like the side of a tree) and are triggered by movement, enabling researchers to identify the species passing by.
The researchers obtained photos from five Canadian national parks and from private land in Montana, as well as data from the San Juan mountains in Colorado. Assembling a database of over 11,000 photos, they painstakingly filtered out 1,534 of them. "That first sorting of images is just to be sure we're only looking at good pictures," says Larkin. Each photographed hare got a score for the percentage of white hair in its coat, which was then compared with the colouration of its background.
Like Dr. Mills and Zimova had discovered, the camera trap data detected that hares are mismatched with their surroundings for a period of time each spring and fall. The mismatch was particularly striking during a late snowfall at the start of June 2011, when the hares' darker coats turned them into easy pickings for predators, explains Larkin.
So, does mismatched timing spell trouble for the hares in a warming and less snowy world? Work in progress by Dr. Mills and Zimova suggests the answer is yes: hares that match their background better have higher survival rates than those that stick out like dinner on a white plate.
And there're more bad hare news. The duo's previous work suggests the animals aren't good at adjusting their behaviour to reduce mismatch, by hiding or selectively choosing backgrounds that match better, for example. "[As a species], they don’t seem to be very smart," Zimova laughs.
The story of the snowshoe hare, just like the timing of its colour change, is still evolving. But one thing is clear: natural selection will be a strong force in this story, pushing the species to adapt to a shorter period of snow cover. Those that fail to blend in are likely to land up on top of the menu for hungry carnivores.
Top header image: Denali National Park and Preserve, Flickr
