In the mountains of Nagano Prefecture, in central Japan, there is a valley where the winters are long and brutal — temperatures dropping to minus 15 degrees Celsius, snow lying metres deep, the landscape locked in a cold that would be lethal to most primates. And yet, every winter, a troop of Japanese macaques descends to the valley’s volcanic hot springs, wades into the steaming water, and sits — eyes half-closed, faces relaxed, apparently content — while the snow falls around them.
The image of the Japanese macaque (Macaca fuscata) soaking in a hot spring has become one of the most iconic wildlife photographs in the world — a picture of an animal that looks, in that moment, uncannily human. It has appeared on the covers of magazines, in documentaries, in advertising campaigns, and in countless wildlife photography books. It is the image that most people think of when they think of Japan’s wildlife.
But the hot spring bathing is only the beginning of the Japanese macaque’s story. Beneath the charming surface of a monkey in a thermal bath lies one of the most scientifically significant primates on Earth — an animal that has taught researchers more about animal culture, social learning, and behavioural innovation than almost any other species.
The Northernmost Monkey
The Japanese macaque is the most northerly non-human primate on Earth. While most primates are confined to tropical and subtropical regions, the Japanese macaque has extended its range into the temperate forests of Honshu, Shikoku, and Kyushu — and into the subarctic conditions of northern Honshu and the Shimokita Peninsula, where it survives winters that would be impossible for any other primate species.
This cold-weather adaptation is reflected in the macaque’s physical characteristics. Its fur is thick and dense — much thicker than that of tropical macaques — providing insulation against temperatures that can drop well below freezing. Its face is bare and red — the redness produced by blood vessels close to the skin surface, which flush with blood during social interactions and temperature regulation. And its body is compact and robust, with relatively short limbs that minimise heat loss in cold conditions.
The Japanese macaque’s ability to survive in cold environments is not purely physiological — it is also behavioural. The animals have developed a range of cold-weather strategies, including huddling together for warmth, reducing activity during the coldest periods, and — most famously — using geothermal hot springs for thermoregulation.
The Hot Spring Discovery
The hot spring bathing behaviour was first documented at Jigokudani — “Hell Valley” — in Nagano Prefecture in 1963, when a young female macaque named Mukubili waded into a hot spring to retrieve a soybean that had fallen into the water. She found the warm water pleasant and began bathing regularly. Other young macaques, observing her behaviour, began to imitate it. Within years, the behaviour had spread through the troop and become a cultural tradition — passed from mothers to offspring, maintained across generations, and now so firmly established that it is considered a defining characteristic of the Jigokudani troop.
This is cultural transmission — the spread of a learned behaviour through a social group by observation and imitation, rather than by genetic inheritance. It is the same process by which human cultures transmit knowledge, skills, and traditions across generations. And its documentation in Japanese macaques — along with similar observations in other primate species — fundamentally changed the scientific understanding of animal cognition and culture.
The Sweet Potato Washer
The hot spring bathing is the most famous example of Japanese macaque cultural innovation, but it is not the first. That distinction belongs to a young female named Imo, living in a troop on the island of Koshima in the 1950s.
In 1953, researchers from Kyoto University began provisioning the Koshima troop with sweet potatoes, placing them on the beach to attract the monkeys for observation. The potatoes were covered in sand, which the macaques found unpleasant. In 1953, Imo — then approximately one and a half years old — was observed carrying a sweet potato to a stream and washing the sand off before eating it. She had invented a new behaviour — one that no macaque had been observed performing before.
Over the following months and years, the behaviour spread through the troop. Imo’s playmates learned it first, then their mothers, then other adults. Within a decade, most of the Koshima troop was washing sweet potatoes — and some individuals had refined the behaviour further, washing their potatoes in the sea rather than fresh water, apparently preferring the salty flavour.
Imo later invented a second innovation: separating wheat from sand by throwing handfuls of the mixture into the water and skimming the floating wheat from the surface. This behaviour also spread through the troop by social learning.
Imo’s innovations became one of the most cited examples of animal culture in the scientific literature — evidence that non-human animals could invent new behaviours, transmit them socially, and maintain them as cultural traditions across generations. The implications for our understanding of the uniqueness of human culture were profound and are still being debated.
Social Life in the Snow
Japanese macaques live in troops of 20 to 100 individuals, organised around a core of related females who remain in the troop for life. Males disperse at sexual maturity, moving between troops and occupying peripheral positions in the social hierarchy. The troop is led by a dominant male — the alpha — who maintains his position through a combination of physical dominance and social alliances.
Social bonds within the troop are maintained through grooming — the meticulous removal of parasites, dead skin, and debris from another individual’s fur. Grooming is not merely hygienic — it is the primary currency of social relationships in macaque society, used to establish and reinforce alliances, reduce tension after conflicts, and signal social status. The amount of time an individual spends grooming and being groomed reflects its social position and the strength of its relationships.
Japanese macaques have a rich repertoire of vocalisations — including specific calls that communicate information about food, predators, and social situations. They show evidence of individual recognition — responding differently to the calls of familiar and unfamiliar individuals — and of understanding social relationships between third parties, a cognitive ability that was once thought to be uniquely human.
The Conservation Success Story
The Japanese macaque is, in the context of primate conservation, a rare good news story. Its population — estimated at approximately 114,000 individuals — is stable or increasing, and it is listed as Least Concern on the IUCN Red List. It is the only primate in Japan, and it has benefited from strong legal protection, a cultural tradition of reverence for wildlife, and the absence of the large-scale deforestation that has devastated primate populations elsewhere in Asia.
The macaque’s relationship with humans in Japan is complex and not always harmonious. In agricultural areas, macaques raid crops — eating vegetables, fruits, and grains — causing significant economic losses for farmers. Human-macaque conflict is a persistent management challenge, and macaques are sometimes killed as agricultural pests. The management of this conflict — balancing the needs of farmers with the protection of a culturally significant and legally protected species — is an ongoing challenge for Japanese wildlife managers.
The Jigokudani Monkey Park, where the hot spring bathing troop lives, has become one of Japan’s most popular wildlife tourism destinations — attracting hundreds of thousands of visitors annually and generating significant economic value for the local community. The park demonstrates how wildlife tourism can create economic incentives for conservation, turning a wild animal into a community asset rather than a pest.
What the Snow Monkey Teaches Us
The Japanese macaque has contributed more to our understanding of animal cognition and culture than almost any other primate species. Imo’s sweet potato washing, the hot spring bathing, and dozens of other documented behavioural innovations have demonstrated that the capacity for cultural transmission — once thought to be uniquely human — is shared with other primates, and perhaps with many other animals.
This has profound implications for how we think about human uniqueness, about the nature of culture, and about the moral status of animals. If culture — the transmission of learned behaviours across generations — is not uniquely human, then the boundary between human and animal cognition is less sharp than we once believed. And if animals have cultures, then the loss of a population is not just a genetic loss — it is a cultural loss, the extinction of a unique set of traditions and innovations that may have taken generations to develop.
The snow monkey soaking in its hot spring is not just a charming photograph. It is a window into the cognitive complexity of a species that has been surprising scientists for seventy years — and that continues, in the snowy mountains of Japan, to invent, to learn, and to pass its knowledge on.
Go Deeper
The complete story of the Japanese macaque — its biology, cultural innovations, social life, and conservation status — is covered in our premium Japanese Macaque Wildlife Guide.