Climate crisis: Less snow means mountain hares’ winter coats no longer camouflaged, study warns

Animals unable to match pace of environmental change, leaving them vulnerable to predators

A mountain hare in Scotland. Lack of snow is leaving the animals exposed on the dark heather-covered mountains and hillsides of the Highlands (Getty)

The climate crisis could spell disaster for Scotland’s mountain hare population as less snowy winters mean the animals’ natural seasonal change from brown to white - to make them more camouflaged - is having the opposite effect.

As the duration of snow cover is decreasing, this creates a seasonal “mismatch”, which exposes the hares to predators, and the species is failing to adapt the timing of these seasonal moults to keep pace with the climate crisis, a new study shows.

A team of scientists led by Marketa Zimova, an evolutionary ecologist at the University of Michigan, first examined horseshoe hares in the US, which also change colour when they moult.

They found that “camouflage mismatched hares suffer much higher predation rates. We also found that the increase in mortality due to mismatch will, in the absence of an adaptive shift, lead to population declines by 2100.”

In order to assess mountain hares in the UK, the team used data going back to the 1950s and 60s detailing changing moult timings - or “phenological shifts” of mountain hares in Scotland, and compared them to the timings today.

The research team said due to the existence of these earlier studies they could make the research the longest running systematic historical survey of moult phenology in any species.

They returned to the Scottish Highlands to carry out surveys and record the pattern and timing of moult over multiple spring and autumn seasons.

The researchers also calculated the change in temperature and snow cover over the past 65 years within the study region.

Despite what they described as a “dramatic change in climate”, there was little evidence of an adaptive shift in moult phenology in Scotland’s mountain hares - resulting in a mean of 35 more days a year when white hares are found on dark, snowless background since the 1950s.

Scott Newey, an animal ecologist at the James Hutton Institute and co-author of the study, said: “The camouflage mismatch of mountain hares is really surprising and worrying, and suggest that some wild animals can’t adapt quick enough to match the rate of climate change.”

These concerns are shared by L Scott Mills, a professor at the University of Montana and a fellow co-author of the study, who said: “These are important findings because they indicate that some colour moulting species are not responding as we’d expect based on what we’ve seen in other systems.”

The reason that the mountain hare moult phenology has remained relatively static is not clear, but Dr Zimova said the reason might be due to the reduction in the number and diversity of predators associated with land management in large parts of the study area.

Sean Giery, an Eberly fellow from the Pennsylvania State University and also a co-author of the study, said: “It’s an interesting scenario playing out in the Highlands. We saw this really distinct increase in camouflage mismatch that didn’t conform to findings in other ecosystems like Montana.

“It took us a while to realise that what we were seeing – steadily increasing camouflage mismatch in mountain hares – might be the result of an ecosystem subject to climate change, and a history of predator control.

“Without many predators, fitness costs of camouflage mismatch might be minimal."

Dr Zimova notes recent climate change has already subjected wild populations to large change in environmental conditions, and failure of a species to adapt to these changes will ultimately result in decline and extinction.

“If we want species to persist in a rapidly changing world, we need to understand their responses to climate change. This challenge includes considering a suite of anthropogenic changes, and how they interact,” she added.

Mountain hares are the UK’s only native lagomorph species, with rabbits and brown hares both modern introductions.

Mountain hares also face threats from grouse gamekeepers, due to the belief the animals spread a tick which carries a virus called “louping ill” to red grouse.

The research is published in the Proceedings of the Royal Society B.