When snow starts to fall, mountain hares melt into the landscape by shedding their dark fur and turning a brilliant – but camouflaged – white.
But mountain bunnies in Scotland are failing to adapt to a dramatic increase in snowless days, with their white fur on dark mountain slopes making them visible to potential predators.
Some high latitude species have been shown to adapt their moulting times to the rapidly changing climate.
However, a study of mountain hares in Scotland found that they do not change their moulting times at all, leaving them with no suitable camouflage on average 35 days a year compared to 65 years ago.
Historical data from mountain hare flights in the 1950s was compared with the sightings of hares in similar Scottish sites in 2015 and 2016 by a team of scientists in North America and Scotland.
Led by Dr. Marketa Zimova of the University of Michigan, the researchers also analyzed more than six decades of weather data that revealed a drastic decrease in “snowy days” over a similar time period to the study published in Proceedings of the Royal Society B.
They found that between 1960 and 2016, there was an average decrease of 37.14 days of snow cover in their Highlands study spots. In 2016, the average early autumn snow fell four days later, while the late spring snow was, on average, a week earlier than in the 1960s.
For species in snowy environments that change color to avoid predators, such as arctic foxes or ptarmigan, changing day length appears to be the main cause of molting.
But other studies have shown that animals can adapt their molts to keep up with climate change because if they are not left camouflaged, they are vulnerable to predation. In North America, the weekly survival of snowshoe hares decreased by 7-14% when the animals did not match their backgrounds. Increased predation rates also occurred among mismatched mountain hares in Norway.
But despite strong evolutionary pressure on animals to adapt to snowless conditions, the scientists found no such adaptation in the Scottish mountain hares.
In the 1950s, the hares were given their winter coats at the end of October, and in the spring, around mid-March, they matured again. They continued to moult at the same time until the 2010s.
According to the scientists, the hares’ failure to adapt their molts when other animals in different environments do may be due to a lack of natural predator pressure in Scotland, a lack of genetic diversity among mountain hare populations, or the speed of climatic changes. .
Scott Newey of the James Hutton Institute, a co-author of the study, said, “The fact that mountain bunnies don’t adjust moulting is really quite surprising. The mountain bunny population may not have the diversity within the gene pool to adapt and make changes, or it may be that the change in snow location is too rapid.
“The third hypothesis is that the studies were conducted in areas managed for grouse shooting and grouse shooting is associated with predator control, particularly foxes and crows, which are legally controlled.”
Now that the grouse shooting industry has suppressed populations of natural predators, including feral cats and golden eagles, for more than a century, there may not be urgent evolutionary pressure on mountain hares to adapt their color to the surrounding conditions, as hares do not match their environment. , can survive.
But the study warns that if predators return – with the reduction in grouse shooting, for example – mountain hare could be vulnerable to the population decline because they haven’t adapted their riding to remain camouflaged.