Two hares, two very different relationships with winter — and one of them is starting to miss the snow.
Japan has two kinds of wild hare, and they don't handle winter the same way. On Honshu, Shikoku and Kyushu, the Japanese hare grows a white coat in some mountain regions and stays brown all year in others — with no genetic difference between the two groups. Up in Hokkaido, a separate species always turns white. New research on that Hokkaido population found something worth worrying about: its winter coat is starting to arrive out of step with the snow. (We'll teach you the Japanese words as we go.)
Some populations turn white. Others just don't.
冬毛 — fuyuge (winter coat)
The Japanese hare, Lepus brachyurus (ノウサギ, no-usagi), lives across the mountains and hills of Honshu, Shikoku and Kyushu — everywhere except Hokkaido. Of its four subspecies, only two grow a white fuyuge for winter; the other two stay brown year-round. The white-coated populations moult from mid-September to late November, then shed the white and moult back to brown from late January into spring. Where you find a hare that turns white and where you find one that doesn't is mostly a matter of geography and typical snow cover — not a strict north-south line, since some snowy inland ranges have brown-coated populations too.
White and brown populations aren't genetically split
換毛 — kanmō (moulting, coat change)
Here's the part that surprised researchers: when population genetics work compared white-changing and non-changing groups of L. brachyurus, it found no consistent genetic divergence between the two coat-color morphs. In other words, "does this population do a white kanmō or not" doesn't map cleanly onto separate genetic lineages. The trait behaves more like a flexible, locally tuned response — plausibly shaped by day length and local climate history — than like two hares that have been evolving apart from each other for a long time.
The Ezo mountain hare always turns white — and the timing is slipping
雪 — yuki (snow)
Hokkaido has no L. brachyurus at all. Its hare is a different species, the Ezo mountain hare (Lepus timidus ainu), a subspecies of the mountain hare found across northern Eurasia. Unlike its mainland cousin, it reliably turns white every winter. A 2026 study in Ecology and Evolution tracked its spring and autumn moults at a site in Hokkaido across years with very different yuki conditions, and found a mismatch: the hare's coat-color schedule is driven mainly by day length, but snow cover in Hokkaido is arriving later and melting earlier than it used to. A white hare against bare ground — or a brown one against early snow — stands out to predators in exactly the season it can least afford to.
So which is the "normal" Japanese hare strategy?
There isn't one — and that's the actual finding. Mainland Japan runs a flexible experiment where whole populations can apparently switch a costly trait on or off without splitting into separate genetic groups, tracking local snow reliability instead of a rigid rule. Hokkaido runs the opposite strategy: a hard-wired, day-length-triggered white coat that assumes the snow will be there when the fur turns. That second strategy worked for a long time because photoperiod and snowfall used to move together. The 2026 research is one of the more current, concrete data points showing that assumption breaking down — and it's not just hares: coat-color mismatch has separately been linked to population declines in snowshoe hares, other mountain hare populations, and rock ptarmigan (a Japanese alpine bird whose own seasonal moult we've covered before). A trait that looks like a fixed rule of nature can turn out to be a bet on a climate that no longer holds.
Common questions
Q. Do all Japanese hares turn white in winter?
A. No. Of the four subspecies of the Japanese hare (Lepus brachyurus) found on Honshu, Shikoku and Kyushu, only two grow a white winter coat; the others stay brown all year.
Q. Is the white-coated population a genetically separate group from the brown one?
A. Research comparing population genetics found no consistent genetic split between the white-changing and non-changing groups, suggesting the trait is a flexible, locally shaped response rather than a fixed lineage difference.
Q. Is Hokkaido's white hare the same species as the mainland Japanese hare?
A. No. Hokkaido's hare is the Ezo mountain hare (Lepus timidus ainu), a subspecies of the mountain hare found elsewhere across northern Eurasia. It reliably turns white every winter, unlike the mainland species.
Q. What did the 2026 study on Hokkaido's hare find?
A. Comparing moult timing across years with different snow conditions, the study found the hare's coat-color change (largely triggered by day length) is increasingly out of step with when snow actually arrives and melts, creating camouflage mismatch.
Q. Why does camouflage mismatch matter for a hare's survival?
A. A hare whose coat color doesn't match its background is more visible to predators. This kind of seasonal mismatch has been linked to population declines in several other coat-color-changing or moulting species as well.
Where to find Japan's wildlife in the wild: our region-by-region wildlife guide. Or explore all 47 prefectures by recorded species in Ikimono Quest, built from open biodiversity data.
Written by naturalists. The science here reflects published research on population genetics and coat-color polymorphism in the Japanese hare (Lepus brachyurus), and a 2026 study in Ecology and Evolution on seasonal coat-colour moult phenology and snow-cover mismatch in the Ezo mountain hare (Lepus timidus ainu) in Hokkaido. Species identification is of real, extant mammals native to Japan. Nature is full of exceptions — that's what makes it worth studying.