MISSOULA – The predicted decrease of winter snowpack due to climate change might inconvenience winter recreationists, but for mammals that change coat color during the cold months to blend in and survive, the consequences could be much graver.
L. Scott Mills, a professor in The University of Montana College of Forestry and Conservation, will publish an article titled “Camouflage Mismatch in Seasonal Coat Color Due to Decreased Snow Duration,” in the April issue of Proceedings of the National Academy of Sciences. The article will detail research on the snowshoe hare, one of 10 animal species worldwide that changes color from brown to white to match seasonal snow cover.
Mills and his colleagues studied wild hares for three years in western Montana. The study examined 148 hares weekly in the field to quantify their coat color, the extent of snow around them and the percent of mismatch between the hare and their background. The three years during the study included some of the most extreme differences in snowpack duration that have occurred in the past 40 years, including the incredibly long 2010-11 snow season and the much shorter season the year before.
The results of the study link the seasonal coat-color change across different years to the prospect of less snow in the future.
Though the timing of the molt did not change in either the fall or spring for the hares in the study, the rate at which they changed did vary, but only in the spring molt.
Hares in the fall changed purely based on the length of the day, but the hares changing in the spring were able to slow the rate of their molt in the heavy snow year of 2010-2011.
“On average, it takes about 40 days for a hare to completely change from brown to white,” Mills said. “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.”
Animals that change color seasonally may adapt in two ways to environmental stressors such as reduced snow. If mismatched coat color leads to increased predation, evolution by natural selection will favor hares that can adjust the timing or speed of the change according to snow conditions.
The second adaptation involves the ability of individuals to adjust behaviorally to conditions. The article cites the male rock ptarmigan, a bird that soils its feathers after mating in an apparent attempt to camouflage, as one example of behavioral adaptation.
The next step for Mills’ research group is to document whether mismatch in the hares’ coat color does in fact increase predation and whether adaptation is occurring.
“Hares that are mismatched may minimize mortality by seeking out snow or remaining in dense cover, and the potential for rapid evolutionary change in timing of coat color cannot be discounted,” Mills said.
The researchers also developed rigorous snow models for the future, accounting for uncertainty by averaging scenarios across 38 different climate models. When they applied the snow models to their snowshoe hare study area, they predicted the average duration of snowpack will decrease by 29 to 35 days by mid-century and 40 to 69 days by the end of the century.
They found that this decrease in snow would lead to a four- to eight-fold increase in the number of days that white hares will be mismatched on a brown, snowless background, making them vulnerable to predators.
Whether hares can adapt, either by natural selection, behavioral adaptation or both, has major implications for the species. As the climate models show, the change will need to come quickly.
For the snowshoe hare, an essential prey for the threatened Canada lynx, and an animal experiencing 85 to 100 percent mortality due to predation, the ability to be camouflaged is a critical defense. Because seasonal coat color change occurs for species throughout the world, the prospect of white animals on brown backgrounds serves as a widespread stark image for the impact of climate change.
The article co-authors are UM graduate students Marketa Zimova and Jared Oyler, Regents Professor of Ecology Steve Running and Assistant Professor Paul Lukacs, all of the College of Forestry and Conservation.