The mountain hare struggles with colour as the climate changes

The mountain hare changes from white in winter to brown in summer. The hare's goal is to blend in as much as possible with its surroundings.

For the first time in Norway, it has been documented that the hare cannot adapt as quickly as the climate changes.

“We investigated the correlation between shorter winter duration over the past 60 years and the timing of coat colour change in hares. We found that areas experiencing the greatest decrease in number of days of snow-cover during winter were the areas where hares had the wrong colour for the most days throughout the year,” says Allan William Stokes.

Stokes recently defended his doctoral thesis on this topic at Inland Norway University of Applied Sciences (INN University).

Plenty of photographic evidence 

A significant part of the work involved classifying approximately 10,000 images of hares captured by the Norwegian Institute for Nature Research's 700 camera traps across large parts of Norway. These photos span over the last ten years.

“We have an enormous amount of data, and we are very pleased to have had access to these photos. It has been a massive task, and we have received help from students and interns who have been classifying all these photos,” says Stokes.

With these photos, Stokes has been able to directly study the hares passing the cameras in both summer and winter. He could assess the hare's coat colour and whether there was snow on the ground or not. 

“Why do you think no one has written a doctoral thesis on this before?”

“It would not have been possible to gather enough data to calculate the timing of coat changes across Norway using conventional techniques, such as capturing, marking, and tracking individuals,” he says.

The development of wildlife cameras makes collecting the data necessary for this type of study much easier, the researcher adds. 

Clearly demonstrates climate change

The doctoral thesis shows a wide variation in Norway regarding how many days the hare has the wrong colour.

Many areas no longer have continuous snow cover throughout the winter. Especially along the southern coast, hares have the wrong colour for long periods. In inland areas and at higher altitudes, they have the wrong colour for the fewest days.

“We have suspected this, but this is the first time it has been documented precisely when this happens, and that we have seen this pattern,” says Simen Pedersen.

Pedersen is an associate professor at INN University's Department of Forestry and Wildlife Management, and was Stokes' supervisor.

“What are the consequences of the hare not being able to keep up with climate change?”

“We assume that if you're white on bare ground, you're more visible to predators and thus more vulnerable. We don't have specific numbers on this, but we have an ongoing marking project where we will examine survival rates based on coat colour to determine this as well,” he explains.

Is the hare able to adapt?

The mountain hare in Norway does not change the timing of its coat change as quickly as the climate changes.

However, there is hope for the hare in the future. Stokes explains that in Norway, we have a subspecies of mountain hare that may have adapted in ways worth noticing.

“A hare called the heath hare changes to a blue-grey coat in winter instead of snow white. This adaptation is believed to be suited to milder winters with variable snow cover, as hares with this coat colour are more likely to be camouflaged in areas with limited snow cover,” says Pedersen. 

There are 21 different species worldwide that change their coats from winter white to summer brown, and vice versa.

Researchers at INN University will further investigate whether hares are making behavioural adaptations to their new environment. 

Research by Simen Pedersen and colleagues from Scotland and the USA suggests that mismatched hares in Scotland do not make behavioural changes; they are not aware of their own colour. It is uncertain how applicable this finding is to Norwegian conditions.

“When it comes to climate change, it's possible that hares may adjust the timing of their coat change. But so far, we have found that hares don't adapt as quickly as the climate changes and winter becomes shorter,” Pedersen explains.

“What does this research mean for your doctoral thesis?”

“In the broader context, this research illustrates the likely impact of future climate change on many species,” concludes Stokes.

Reference:

Stokes, A. Climate change and the race for survival: exploring the effects of climate change on the phenology and distribution of native mountain hares (Lepus timidus) and invasive European hares (Lepus europaeus), Doctoral dissertation at Inland Norway University of Applied Sciences, 2024.

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Read the Norwegian version of this article on forskning.no

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