Global warming is threatening the survival of the common stoat – because its winter coat is no longer an advantage in the milder weather.

The Dutch mammal society Zoogdiervereniging has designated 2024 its “year of the stoat” because of concerns that its numbers are in decline because of a combination of urbanisation, pesticides and climate change.

The stoat is unique among creatures in the Netherlands in that it grows a pure white coat in winter to blend into the snowy landscape – in contrast to the rest of the year when its upper body is brown.

But in recent winters so little snow has fallen – none has been recorded in the past months – that a feature that evolved as a type of camouflage now has the opposite effect.

A study by Dutch researchers in northern Sweden, where stoats also change colour in winter, found that white stoats attracted more predators than decoys that mimicked the furry mammals’ summer colouring.

“You’d expect to see stoats being less successful at hunting in winter and, moreover, becoming more vulnerable to being hunted themselves,” researcher Joris Cromsigt said.

Maurice La Haye of Zoogdiervereniging said the fact that the stoats still grow white coats in winter colour suggests that the change is triggered by the shortening winter days rather than falling temperatures.

That makes it difficult for the stoats to adapt to the changing conditions. “The length of the day remains the same even if the temperatures rise,” La Haye said.

However, researcher Carola van den Tempel said “time will tell” if the stoat can overcome the challenges of climate change. “If some stoats remain brown in winter, they will prevail through natural selection,” she said.