Japanese Macaque
The Japanese macaque (Macaca fuscata), known around the world as the snow monkey and in Japan as nihonzaru, is Japan's only native monkey and the primate, apart from humans, that lives farthest north and in the coldest climate. It is found on Honshu, Shikoku, Kyushu and several smaller islands, from the subtropical forests of Yakushima to the snowy mountains of the Shimokita Peninsula, where winter temperatures can fall to about minus 20 degrees Celsius. It has a bare pinkish red face, a short stump of a tail and thick brownish gray fur that grows denser as the weather turns cold. Troops are built around lines of related females, who stay in the troop where they were born, while males leave before they mature. Its diet changes with the seasons and includes more than 200 kinds of plants, as well as insects, bark and soil. The macaques of Jigokudani, in Nagano Prefecture, became famous for soaking in hot springs in winter, a habit first seen in 1963 and learned by copying others, not by instinct. The IUCN lists the species as Least Concern with a stable population, although more than 20,000 are culled every year because of damage to crops.
What is a snow monkey? Meet the Japanese macaque
Snow monkey is the popular name of the Japanese macaque, Macaca fuscata, a monkey of the macaque genus described by the English zoologist Edward Blyth in 1875. In Japan it is called nihonzaru, or simply saru, and it is the only monkey native to the country. Its fame comes from where it lives: no other primate except humans lives farther north or in a colder climate, and in the mountains of central and northern Honshu it spends months surrounded by snow. Scientists recognize two subspecies. The common form, Macaca fuscata fuscata, lives on Honshu, Shikoku, Kyushu and nearby islands. The Yakushima macaque, Macaca fuscata yakui, lives only on Yakushima Island, south of Kyushu, and is smaller, with darker and thinner fur suited to a warm, very rainy forest. A survey completed in 1999 estimated between 9,500 and 19,000 of them on the island. The Japanese macaque is one of the best studied primates in the world. Japanese researchers began following wild troops in the late 1940s and early 1950s, giving names to individual monkeys and recording their family lines, and much of what is known about learned traditions in animals comes from this work.
How big is a Japanese macaque?
The Japanese macaque is a stocky, medium sized monkey. Adult males average about 57 centimeters in height and 11.3 kilograms, while females average about 52 centimeters and 8.4 kilograms, and macaques from colder regions tend to be heavier than those from the warm south, which helps them hold heat. The tail is a short stump: about 9 centimeters long in males and 8 in females, far shorter than in most macaques, so less body heat escapes through it. The fur is brownish gray, longer and denser in winter, and it gives the snow monkeys of Nagano their round, fluffy look in photographs. The face and rump are bare and pinkish red. The color comes from blood vessels close to the skin and grows stronger in adults, and in the mating season the faces of both males and females turn a deeper red. Babies are born with dark brown hair and a paler face. Despite their bulk, Japanese macaques are agile climbers and strong swimmers, and they have been seen swimming more than half a kilometer. Females spend more time in the trees, while males spend more time on the ground. Their brain weighs about 95 grams.
Where do snow monkeys live?
Japanese macaques live only in Japan, on three of its four main islands, Honshu, Shikoku and Kyushu, and on several smaller islands such as Yakushima, Kinkasan and Shodoshima. They are absent from Hokkaido, which lies north of Blakiston's Line, the boundary across the Tsugaru Strait that also marks the limit of other southern animals. The northernmost population lives on the Shimokita Peninsula in Aomori Prefecture, at the tip of Honshu, at about 41 degrees north, roughly 500 kilometers north of the famous troop at Jigokudani. Few primates cope with such a range of climates. In the south, macaques live in warm evergreen broadleaf forests close to the coast, and on Yakushima they climb from the shore into dense, mossy cedar forests. In central and northern Honshu they live in cool deciduous forests of beech and oak, where snow can cover the ground for four months a year. The IUCN gives an elevation range from sea level to 1,500 meters, and it lists the range as stable and not fragmented. Some troops have settled near towns and farms, and well known groups live at Takasakiyama in Oita, Arashiyama in Kyoto and Kinkasan in Miyagi.
Why do snow monkeys bathe in hot springs?
The bathing snow monkeys of Nagano are a fairly recent tradition. In the winter of 1963, a young female macaque was seen soaking in an outdoor hot spring that belonged to an inn near Jigokudani, the Korakukan, and other monkeys soon copied her. Young animals picked up the habit first and adults followed, and it passed from mothers to their young until it became normal for the troop. Because monkeys in the inn's bath raised hygiene concerns, the Jigokudani Monkey Park built a hot spring pool just for them, and that pool is the one seen in so many photographs. The habit is learned, not instinctive, and most Japanese macaques never bathe. A study published in 2018 in the journal Primates measured stress hormones in the droppings of adult females at Jigokudani and found that bathing in winter lowers stress, likely by helping them save energy in the cold. It also found that higher ranking females spent more time in the water, while lower ranking ones were often kept out. Bathing is not without cost: wet fur loses heat fast, so the macaques stay close to the warm water and groom each other when they climb out. Monkeys in onsen are now one of Japan's best known winter images.
Jigokudani Snow Monkey Park: where to see them
Jigokudani Yaen Koen, the Snow Monkey Park, is in the town of Yamanouchi in Nagano Prefecture, in the valley of the Yokoyu River inside Joshinetsu Kogen National Park. Jigokudani means Hell's Valley, a name that comes from the steam and boiling water that rise from the ground. The park sits at about 850 meters and has welcomed visitors since 1964. It was born from a conflict: in the 1950s, ski resorts and forest clearing in the Shiga Kogen mountains pushed the macaques into villages, where they raided crops, and feeding them in the valley drew them away from the fields. The monkeys are wild and come and go from the forest, but attendants feed them, so they can be seen all year. Winter, from about December to February, is when the valley is under snow and the macaques use the hot spring pool most. The park can only be reached on foot, by a forest path of about 2 kilometers, and the nearest towns are the hot spring resorts of Yudanaka and Shibu Onsen, about three and a half hours from Tokyo. Visitors must not touch, feed or stare at the monkeys, and must keep food and plastic bags out of sight.
How do Japanese macaques survive the cold?
Japanese macaques cope with winter temperatures as low as about minus 20 degrees Celsius, colder than any other monkey faces. Their first defense is the coat: in autumn the fur grows longer and much denser, trapping a layer of warm air against the skin. The short tail and the heavier bodies of northern macaques also help them lose less heat. Behavior does the rest. On cold nights and snowy days, members of a troop sit pressed together in tight huddles, and these huddles are built mostly among relatives and close companions. They also store energy: in autumn they eat large amounts of nuts, acorns and seasonal fruits to build up fat before the snow arrives. In winter, when leaves and fruit are gone, northern troops survive on bark, buds, twigs and roots, digging through the snow to reach them, and they move less to save energy. Hot spring bathing at Jigokudani is a local extra rather than a survival need for the species. Young macaques even seem to enjoy the snow: they have been seen rolling snowballs, carrying them around and playing with them, a behavior that appears to be simple play.
What do Japanese macaques eat?
The Japanese macaque is an omnivore with a mostly plant diet, and more than 213 species of plants have been recorded in its menu. It also eats insects and other invertebrates, bark, flowers, some nectar and even soil, and when its preferred foods are scarce it digs up roots and rhizomes and has been seen eating fish. What it eats depends on the season and the place. In spring it feeds on young leaves, buds and flowers. In summer and autumn it turns to fruits, seeds, nuts and acorns, putting on fat for the winter. In winter, northern troops rely on bark, twigs, winter buds and roots, while on Yakushima macaques eat fruit, mature leaves, fallen seeds, fungi and ferns. On Kinkasan Island they eat fallen seeds, herbs, young leaves and fruit, especially Japanese barberry and Japanese zelkova. They feed two to four times a day in winter and two to three times in spring and summer. Some food habits are cultural. On Koshima Island in the 1950s, a young female named Imo began washing sweet potatoes in a stream and later in seawater, and the habit spread through her troop over generations. She also learned to separate wheat from sand by throwing it into the water.
How do snow monkeys live in troops?
Japanese macaques live in troops that usually hold a few dozen animals, though troops that are fed by people can grow much larger: the main troop at Takasakiyama, in Oita, numbered 677 monkeys in 2021. Each troop is built around several lines of related females, ranked in a strict order. Daughters inherit a rank just below their mothers, and younger sisters usually outrank older ones. Males leave the troop where they were born before they mature, and many spend long periods alone or in all male groups before joining another troop. Males have their own hierarchy with one alpha, and rank tends to rise the longer a male stays. In 2021 a nine year old female named Yakei became the leader of the Takasakiyama troop, the first female leader there in some 70 years of records. Grooming fills much of the day, and calls such as soft coos keep the troop together while foraging. Researchers have even found local accents, with call pitch differing between areas. Mating takes place in autumn and winter, when faces and rumps turn bright red. Pregnancy lasts about 173 days, and a single infant is born in spring or summer, mostly from April to June. The baby rides on its mother's belly, later on her back, and is weaned by about 18 months.
Are Japanese macaques endangered?
No. The IUCN lists the Japanese macaque as Least Concern. Its latest assessment, made in November 2015 and published in 2020, describes a stable population that is not severely fragmented, with a generation length of 12 to 13 years. There is no recent national count: a 1989 study estimated 114,431 wild macaques, and numbers have grown since hunting was banned in 1947, helped by more forest cover and the extinction of the Japanese wolf. Success has brought conflict. As macaques move into farmland and towns, they damage crops worth hundreds of millions of yen each year, about 770 million yen in 2024, and more than 20,000 are culled every year under pest control programs, which some scientists fear is shrinking the range in places. In 2022, at least 50 people were attacked by macaques in the city of Yamaguchi. Another threat comes from introduced monkeys. Rhesus macaques released on the Boso Peninsula in Chiba and Taiwanese macaques in Wakayama have crossbred with the native species, and since a 2013 revision of Japan's invasive species law, hybrids are designated for removal; Chiba has run an eradication plan since 2007. Protected areas such as Joshinetsu Kogen and Yakushima also shelter important populations.
