Snowshoe Hares — The New Global Warming Poster Animal?
Seasonal camouflage may become a liability as the seasons change
Meet the snowshoe hare. The hare is one of only ten mammals that have evolved the special skill of seasonal camouflage. Like the arctic fox, the long-tailed weasel, and several other hare species, the snowshoe hare molts from brown to white during winter and then molts back to brown in the spring.
Photos by L. Scott Mills
But this impressive survival strategy could become a liability as global climate change makes the seasons less predictable — leaving the snowshoe hare increasingly mismatched to its surroundings. Unless it’s able to adapt, the snowshoe hare might join the polar bear as an iconic species doomed by global warming.
Research led by University of Montana professor L. Scott Mills and his graduate student Marketa Zimova suggests that this mismatch may have profound effects on predation rates of this animal, which already accounts for close to 85 percent of hare mortality. The hare is an important food source for the threatened Canada lynx, as well as coyotes, fishers, martens, and owls. In the short term, a seasonally mismatched hare would mean an easy feast for these predators. But in the long term, it could mean less food for predators, creating a negative cascade through the ecosystem.
Mills and his team spent the last three years live trapping and radio collaring 148 snowshoe hares near Seeley Lake, Montana. The team made weekly visits to record when the hares began to change color, to see if they were mismatched to their background, and if populations slowed or sped up their change based on snowpack or temperature.
The researchers made some exciting discoveries. They found that hare populations started changing colors based on photoperiod (day length), and not because of the presence of snow. This raises serious questions for the predicament of the hare, since day length and snow season have remained relatively constant over millennia, but now are in sudden flux.
The good news? In the spring the hares were able to partially reduce color mismatch by adjusting the rate of the molt to the snow conditions.
“The white to brown change takes a few days longer and shows some ability to speed up or slow down according to temperature or snow,” Mills said.
The bad news? Hares in the fall changed from brown to white at the same pace regardless of snow conditions. So hares in the fall could be exposed to more years when they are left mismatched to their background, and so more susceptible to predation. The researchers are now looking at whether mismatched hares do, in fact, experience more predation than hares well matched to their backdrop.
In any case, the hares may be able to evolve through natural selection to avoid that predicament. Mills notes that this could occur not over centuries but within a few generations.
“Selection can happen fast,” he said. “Evolution can happen in real time, and this is possibly the subject of further research.”
Hares could also adapt through behavioral changes. Mills points to the rock ptarmigan as one example of an animal displaying behavioral adaptation. Rock ptarmigans also change from brown to white in the winter, but soil their feathers after mating to camouflage themselves.
The researchers have not determined which, if any, behavioral adaptation hares might be using. Mismatched hares may seek out snow, remain in dense cover or have a heightened sense of awareness, Mills said.
The three winters Mills and his team trekked into the Montana backcountry were some of the most varied in terms of severity in the last 40 years. The 2009-10 winter saw very low snowpack, and the snow melted far earlier than average. The 2010-11 winter could not have been more different, with high snowpack and the snow remaining the latest it had in decades. The 2011-12 winter was closer to average.
These extreme differences in winter conditions gave the researchers exceptional data on how the hares reacted. The hares took an average of 16 days longer to complete their change in the late spring of 2011 than they had the year before.
“That’s when I knew we had something great,” Mills said.
Climate scientists have been predicting overall warming for western Montana, but Mills and his team wanted to dig deeper to find out just what warming meant for the area’s snowpack. After working closely with colleagues at the University of Montana’s Numerical Terradynamic Simulation Group and researchers at University of Idaho, they concluded that the area will see averages of 29 to 35 fewer days with snow on the ground by mid-century, and 40 to 69 days by the end of the century.
With similar predictions of warming throughout the world, animals that change color with the seasons must find ways to adapt or evolve. Researchers expect these species to be some of the first affected because they are so specialized to their environments.
Now imagine a white snowshoe hare sitting on a brown or green background. It certainly doesn’t take a degree in wildlife biology to understand the hare’s vulnerability. As snow comes later and leaves earlier, this may be the new icon of climate change for the Rocky Mountains.