This winter we have a lot of snow in Sweden, but the number of days with snow has, on average, dramatically decreased over the past decades. In a new study, researchers at the Swedish University of Agricultural Sciences (SLU) experimentally compared the risk of detection by predators depending on whether the animal has a brown or white coat during periods with and without snow. The results show that animals with a coat color that does not match the surroundings are more often detected by predators.
Mountain hares, willow ptarmigans and weasels are some of the species that seasonally change the color of their fur and feathers; they are brown in the summer and white in the winter. The change is initiated by changes in daylight, historically linked to the arrival and disappearance of snow. This evolutionary adaptation to the local environment is believed to have evolved to increase survival chances. Despite this, few experimental studies have been conducted to determine if coat color actually affects the risk of detection by predators.
'We wanted to know if the assumption holds. The mountain hare has decreased in number, and we believe that is partly due to the reduction of snow, but experimental studies quantifying the risk of having the "wrong" color were lacking,” says Tim Hofmeester, a researcher at the Swedish University of Agricultural Sciences, SLU, who conducted the study together with researchers from the University of Groningen in the Netherlands.
The researchers placed brown and white decoys made of fake fur in front of wildlife cameras to see if and how quickly they were detected by predators. The experiment was conducted in forests and fields outside Umeå during the spring when the landscape transitioned from snow-covered to snow-free.
The results showed that decoys with a color that did not match the surroundings were more often detected by predators, both brown decoys in the snow and white decoys without snow.
“Species that shift to white winter fur or plumage during winter may face problems in the future as the number of snowy days is predicted to decrease due to climate change,” says Tim Hofmeester.
What might happen to them?
“Some species, like weasel and mountain hare, already have subspecies that do not shift to white winter fur. Likely, these have lower predation pressure during winters with little snow and may expand their range northward. The subspecies that shift to white winter fur may possibly disappear,” says Tim Hofmeester."
More predators detected the decoys placed in forests than in fields. “One reason could be that the experiment was terminated before the migrating birds of prey returned, and another is that foxes, which are common in the area, prefer to move in sheltered environments,” says Pieter Otte, the lead author of the study conducted as a Master thesis at SLU.
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The experimental set-up in the field with on the left a camera trap and on the right one of the decoys. Photo: Pieter Otte
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Otte, P. J., M. Cromsigt, P. G., Smit, C., & Hofmeester, T. R. Snow cover-related camouflage mismatch increases detection by predators. Journal of Experimental Zoology Part A: Ecological and Integrative Physiology. https://doi.org/10.1002/jez.2784