This fluffy little tree-dweller can change its diet, its coat, and even its due date when needed, so it’s no surprise it’s a shapeshifter in Japanese mythology. It’s so good, in fact, that it can cause thunderstorms and horrendous house fires while convincingly blaming something else. Then again, the weather can change its behaviour too.

For instance, after doing the marten-mambo, a female can keep the embryos for almost a year if conditions or food supplies are wanting. In the summer or in warmer forests, scarfing down fruit and insects is preferable, whereas in winter or at chillier, higher altitudes, small birds and mammals take up most of the menu. The Japanese marten even has a seasonal coat, but as Funakoshi et al. found in 2017, it’s not due to grilling or chilling.

Japanese Marten Summer Collection 2018. (Budget line.)

In the summer months, a black head and limbs and a brown body are all the rage, while a pale face and a yellowish (ki-ten) or light brown (susu-ten) coat is the way to go in winter. Despite the different end of year outfits, there’s no genetic reason for this, and it boils down to sunlight exposure and local camouflage: it’s no good being bright when there’s barely any snow around. Of course, having a lovely thick coat of many colours can sometimes catch the wrong kind of attention.

While currently “Least Concern”, the Japanese marten is threatened by feral dogs, logging, possible hybridisation with the larger Japanese sable (in case it fancies an extra bit of “rough”), and those who think its coat looks better on them. Fortunately, it has its own private sanctuary on Tsushima Island, and the martens here are genetically diverse, apparently having romped around here since the Pleistocene age up to 2 million years ago.

Elsewhere in Japan and Korea it’s considered fair game and a possible pest, but its dung does help seed dispersal, and gives conservationists a less stressful way of studying it than, say, capturing the males to measure their testicles. (Yes, this actually happened, and in more than one study.) It can be tricky telling it apart from its similar neighbourhood relatives, and people in ancient times had it just as hard.

Known as a trickster as well as a shape-shifter, in Sekien’s Yokai Encyclopaedia of Japanese legends, the marten could stand on its friends’ shoulders to form a pillar of house-wrecking fire, but its name was written with the “weasel” character instead. The Raiju, or “thunder beasts” of yore have also been described as weasel-like, riding lightning, shrieking, tearing up tree trunks and generally being a terrifying nuisance. Then again they’ve also been pictured as monkeys or winged, so there’s reasonable doubt. Perhaps the only real incriminating evidence comes from the Ainu people, who danced wearing marten-skin accessories when praying specifically for bad weather.

Either way, the marten has weathered many a storm thanks to its opportunistic nature and sensible wardrobe. And being several shades of cute probably doesn’t hurt either.


Latin: Martes melampus

What? Tree-dwelling, weasel-like omnivore whose fur changes colour in winter

Where? Usually mature woodlands in Japan, South Korea and North Korea

How big? Head and body length from 47-54 cm / 18.5-21 “, tail from 17-22 cm / 6.6-8.6 ”

Endangered? Currently Least Concern, and one of its habitats on Tsushima Island is protected.

Probable motto: It wasn’t me, it was a weasel.

They look cute. Do they need my help at all?

Despite their fatal arguments with vehicles, feral dogs, logging and furriers, Japanese martens are protected on Tsushima Island and generally widespread.

There are no specific conservation drives (and the centre on Tsushima Island doesn’t seem to accept donations on the English language site), but the Japan Wildlife Conservation Society throws some love to wildlife across the Land of the Rising Sun.

Just to prove I’m not fibbing:

Adachi, Takayuki et al. 2016. “Seasonal food habits of the Japanese marten (Martes melampus melampus) at Otome Highland, central Japan“. Honyurui Kagaku (Mammalian Science) 56(1):17-25.

Batchelor, John. 2014. “Sympathetic magic of the Ainu: The native people of Japan (folklore history series)“. Read Books Ltd.

Funakoshi, Kimitake et al. 2017. “Annual Molting Cycle and Photoperiods That Affect Seasonal Coat Color Changes in the Japanese Marten (Martes melampus)“. Mammal Study 42(4): 209-218.

Hisano, Masumi, and Deguchi, Shota. 2017. “Reviewing frugivory characteristics of the Japanese marten (Martes melampus)“. Zoology and Ecology 28(1):10-20.

Hisano, Masumi et al. 2018. “Thermal forest zone explains regional variations in the diet composition of the Japanese marten (Martes melampus)“. Mammalian Biology 

Hooper, Rowan. 2003. “Japanese marten“. The Japan Times.

Kamada, Shouko et al. 2013. “Multiple Origins of the Japanese Marten Martes melampus Introduced Into
Hokkaido Island, Japan, Revealed by Microsatellite Analysis”. Mammal Study 38(4):261-267.

Kurose, N. et al. 2005. “Fecal DNA analysis for identifying species and sex of sympatric carnivores: A noninvasive method for conservation on the Tsushima Islands, Japan“. Journal of Heredity, 96(6):688-697.

Martes melampus“. No date. Animal Diversity Web.

Martes melampus“. No date. IUCN Red List of Threatened Species.

Mustelidae“. No date. Animal Diversity Web.

Schwartz, Michael K. et al. 2012. “Conservation genetics of the genus Martes: Assessing within-species movements, units to conserve, and connectivity across ecological and evolutionary time“. In Biology and Conservation of Martens, Sables and Fishers: A New Synthesis. Cornell University Press.

Swancer, Brent. 2014. “The thunder beasts of Japan“. Mysterious Universe.

Tatara, Masaya. 1993. “Notes on the breeding ecology and behavior of Japanese martens on Tsushima Islands, Japan“. Journal of the Mammalogical Society of Japan 19(1):67-74.

Yoda, Hiroko and Alt, Matt (translators). 2016. Japandemonium Illustrated: The Yokai Encyclopaedias of Toriyama Sekien. Dover Publications Ltd.

Zimmermann, Kim Ann. 2017. “Pleistocene epoch: Facts about the last Ice Age“.

Featured image credit: “Japanese marten” by rockptarmigan