What triggers mountain hares to change colour?

Day length is the main trigger, not temperature. As autumn days shorten, hares start turning white, typically completing the change by October or November. Temperature can fine-tune the timing slightly in spring, but the photoperiod remains the dominant signal.

Why are mountain hares white in winter when there's no snow?

Their moult timing is controlled by day length, which hasn't changed, but snow in the Scottish Highlands now arrives about three weeks later than it did in the 1960s. This creates a mismatch where hares turn white on schedule but the snow doesn't show up, leaving them highly visible on bare hillsides.

Can mountain hares adapt to climate change and moult later?

It depends on whether evolution can keep pace. Hares that moult later might survive better and pass on those genes, but evolution works over hundreds or thousands of years while climate change is happening across decades. Some lower-altitude populations already show reduced whitening, so local adaptation is possible with strong enough selection pressure.

Meet the Wild Locals

The Mountain Hare Moult: When Camouflage Arrives Three Weeks Late

Mountain hares turn white for winter, which works brilliantly until climate change makes the snow late and they end up sitting on brown heather looking like small luminous idiots. They're still there in summer, just harder to spot when they're actually the right colour.

11 September 20268 min read