Climate Change Means White-Furred Animals Must Adapt or Go Extinct

This April marked the 400th consecutive month that Earth has had above-average temperatures. This human-caused phenomenon means, among many things, that snow is melting — both earlier and slower. There’s much more to lose here than good ski conditions: Less snow means that the white-furred animals that rely on snow for camouflage no longer have anywhere to hide.

In a study released Thursday in Scientific Reports, a team from the Polish Academy of Sciences show that weasels in the dense and primeval Bialowieza Forest are in trouble, but some of them are doing worse than others. Technically known as the Mustela nivalis, these slender mammals are divided into two subspecies: One that is brown all year round and another that sheds its brown coat in the fall and morphs into bright white. The purpose of this adaptation is to blend in with the snowy forest floor and avoid predators — but, the scientists note, the number of days with permanent snow cover has decreased, and the milky-coated weasels are paying the price.

“It is very probably that in the near future white weasels and stoats will disappear completely from many areas of Northern Europe and North America,” co-author Karol Zub, Ph.D., told The Telegraph. “They will either be replaced by brown morphs or they will evolve and molt later in the season, being only partly white for a relatively short period.”

By evaluating Bialowieza Forest weather data reaching back to 1967, the team shows that, historically, snow cover always vanished around March 16. Now, however, it disappears over three weeks earlier than that. Furthermore, the forest used to have about 80 days with permanent snow cover; now it’s only 30. It’s no wonder that the white weasels that once thrived now often look like the weirdos wearing white at somebody else’s wedding.

The scientists confirmed their hypothesis through two experiments. Between 1997 and 2007, they caught 118 weasels. Fluctuations in the number of weasels they caught each year showed that, by 2007, weasel density was about four to five times lower than it was at the start of the study. The number of white weasels they could catch dropped by 20 percent during winter days there was little snow cover, suggesting to the scientists that they weasels had been seen by predators and killed.

To test whether it was the white weasels were really being targeted, the scientists went to the toy section at Ikea and bought a bunch of stuffed animals, figuring it would be better to sacrifice fake mice than actual wildlife. Shaping the toys up to look a little bit more like weasels, they set them out in the forest during snow-less days, and waited for the “attacking, urinating, sniffing, and observing” by predators. Overall, they recorded 138 model-predator encounters, and 31.9 percent of the time the predators — mostly red foxes and raccoon dogs but sometimes buzzards — went in for the kill. And, just as they feared, the predators consistently went for the white toys instead of the brown ones, confirming that their compromised camouflage was their doom.

The white weasels aren’t the only animals that are in trouble. The survival rate of white snowshoe hares, for example, decreases from 9.8 to 6.5 percent when they’re in snowless landscapes. White arctic foxes are increasingly seen roaming brown and green landscapes, increasing concern about their vulnerability as well.

“In the last decade, the number of studies on the adaptation of mammals to changing environmental conditions has increased remarkably due to rapid climate change,” the scientists write. “Climate change will strongly influence the mortality of the nivalis-type due to prolonged camouflage mismatch which will directly affect the abundance and geographical distribution of this subspecies.”