On October 10, 2017, a trail camera set for monitoring deer in Price County, Wisconsin, photographed a fisher that was entirely white. The camera had been placed on a wildlife trail near Brantwood in mixed forest of balsam fir, poplar, sugar maple, and spruce. The image showed a fisher-shaped animal with the right proportions, the right gait, and the right posture walking through the frame at 9:18 in the morning. Everything about it said fisher except the color. Fishers are dark brown to black. This one was white from nose to tail.
Lucas Olson and Maximilian Allen examined the image and published it in the American Midland Naturalist in 2019 as the first scientifically documented case of leucism in a fisher. The eyes and nose retained normal pigmented color, which ruled out albinism. The condition was leucism, a genetic mutation that reduces melanin production in the fur while leaving the soft tissue unaffected. The animal could see normally. It could smell normally. It could hunt, climb, and kill the way any fisher does. The only thing it could not do was disappear into the forest the way every other fisher in Wisconsin does every time it moves through the trees.
A fisher is a stealth predator. It hunts snowshoe hares by stalking through dense understory. It kills porcupines by circling them for half an hour and biting their unprotected faces. It raids squirrel nests by climbing into the canopy and tearing the nests apart. Every hunting strategy the fisher uses depends on the prey not seeing it until the attack is underway. A dark brown animal moving through dark timber at dawn has an advantage that a white animal moving through the same timber does not. Every squirrel on the branch above a white fisher can see it climbing. Every hare in the understory can see it approaching through the snow-free months when the forest floor is brown and the white animal is the only bright object in the frame.
In winter the calculus shifts. A white fisher on white snow is harder to spot than a dark fisher on white snow. A leucistic fisher in northern Wisconsin may actually have a seasonal advantage during the five months when the ground is covered, an advantage that no normally colored fisher has ever needed because the species evolved to be dark year-round. Whether the Price County animal survived better in winter and worse in summer, or whether the disadvantage was constant, is unknowable from a single photograph.
At the time Olson and Allen published, only 33 cases of leucism in any wild carnivore species had been documented in the scientific literature. The rarity is partly a function of how rarely it occurs and partly a function of how quickly it kills. A leucistic animal that cannot hide from predators or cannot ambush prey tends to die young. The Price County fisher was photographed as a healthy adult, meaning it had survived kittenhood, dispersal, and at least one full cycle of seasons as the most visible predator in the forest. Something about its territory, its prey base, or its individual skill was good enough to compensate for the fact that every animal in the woods could see it coming.

Very cool pic.

That is a cool picture.

That's is very cool.

Interesting animal. The feet and nose seem to be a bit darker, too, so it's probably some kind of dilute mutation.

I collect raw skins of such aberrant mustelids and sample them for full-genome sequencing before having them tanned, to maybe eventually understand how these mutations work.
Last year, a fur buyer from western Russia sent me a pine marten that was very similarly colored - cream with slightly darker feet, nose, and tail tip. I thought the skin was a bit dirty at first but turned out it also had slightly darker guard hair tips.

Amazing ^^^

Nice.

The light-colored marten in this picture was taken about 25 years ago in the interior of Alaska, not far from Fairbanks.