The Japanese macaques of Jigokudani Monkey Park, in the mountains of Nagano Prefecture, are the only non-human primates that have culturally adopted the practice of soaking in hot springs. The behaviour appeared in the late 1960s among a single troop, has since been transmitted vertically through generations, and is now a defining cultural marker of the population. The 2010s Nat Geo segment “Monkey Hot Tub” was part of the broader Wild Japan production. Geography Scout’s primatology fan in residence is Tess Harrow, who spent two field seasons working with primate behaviour research projects (one in Madagascar, one in Costa Rica), and she insisted on writing this one up properly.
The Jigokudani population is now one of the most photographed wildlife groups on Earth — every winter, news outlets globally publish the same shots of red-faced monkeys with snowflakes settling on their heads, eyes closed, sitting up to their shoulders in steaming volcanic spring water. The photographs are striking and the underlying behaviour is genuinely interesting. The park is also a useful case study in the management complications of habituated wildlife and the long-term consequences of provisioning.
The Population: Background
The Jigokudani troop is a population of Japanese macaques (Macaca fuscata), the most northerly-distributed non-human primate in the world. The species ranges across most of Japan from the southern islands up into Honshu, with the Jigokudani population at the cool end of the species’ distribution. The valley sits at around 850 metres elevation in the Joshinetsu Kogen National Park; winter temperatures regularly drop below -10°C and the area receives substantial snowfall (typically 1-2 metres of accumulated depth).
Japanese macaques have evolved several adaptations to cold climate that distinguish them from their tropical relatives. Their winter pelage is dense and long. Their body proportions favour heat retention (relatively short limbs, compact body). Their dietary flexibility allows them to subsist on bark, buds, and pine needles when fruits and insects are unavailable. They are robust, cold-tolerant primates, and the hot-spring behaviour is a cultural addition to an already-impressive set of cold-climate adaptations.
The Jigokudani Monkey Park was established in 1964 by Sogo Hara, a local naturalist who began provisioning the troop with regular food in order to make them more visible to visitors. The decision to provision had long-term consequences — both positive (the troop is now one of the best-studied non-human primate populations in the world) and complicated (the population is artificially supported above what the local habitat would naturally sustain, which has implications for both group dynamics and broader ecology).
The Hot Spring Behaviour: How It Started
The hot-spring soaking behaviour was first observed in 1963, when a young female macaque was reported to have entered the outdoor bathing pool of a nearby ryokan (traditional inn) and stayed in the water. Park records indicate the behaviour spread through the troop over the following years, with juveniles imitating the founding female and the practice progressively transmitting across generations. By the late 1970s, hot-spring use was a regular feature of the troop’s winter behaviour.
The Jigokudani staff eventually built a dedicated monkey-only hot spring (the “saru no onsen”) to keep the macaques out of human-used baths and to provide a stable focal point for both the animals and visiting photographers. The saru no onsen has been the location of essentially all the famous winter monkey-bathing footage and photography of the past several decades.
The behavioural ecology of the soaking is interesting. The macaques use the hot springs primarily during the coldest weather, when the thermoregulatory benefit is greatest. Younger animals soak more frequently than older ones, possibly because juveniles have less effective thermoregulation; mothers with infants soak frequently, sometimes with the infant resting on the mother’s head to keep its fur dry. The behaviour is most intense during the coldest weeks of January and February.
Why It Counts as Culture
“Culture” in non-human animals is a contested term in the academic literature. The strict definition that primatologist William McGrew has defended requires several criteria: a behaviour that is socially transmitted (rather than independently invented by each individual), that is geographically variable (different populations have different versions), that is not better explained by genetic or environmental differences alone, and that persists across generations.
The Jigokudani hot-spring behaviour meets all four criteria. It was socially transmitted (the spread pattern from the founding female through the troop is documented). It is geographically variable (no other Japanese macaque population, including those in similarly cold environments, shows the behaviour). It is not better explained by simple environmental availability (other troops have access to hot springs and don’t use them). It has persisted across at least three generations, including animals that never met the original founding female.
This makes the Jigokudani population one of the better-documented examples of non-human animal culture in the primate literature, alongside the Imo monkey troop’s potato-washing behaviour (also Japanese, also documented from the 1950s onward), the chimpanzee tool-use traditions documented by Jane Goodall and others at multiple study sites in Africa, and the orca foraging dialects in the eastern Pacific. The cultural-transmission framework that grew out of these case studies has reshaped how primatologists think about the boundary between biological evolution and behavioural learning in social species.
The Provisioning Question
The Jigokudani population is provisioned with food by park staff. This is the central management complication of the site, and the question of whether the practice should continue has been debated within the Japanese primate research community for decades.
The case for provisioning: it concentrates the population at a predictable location, which makes long-term research and monitoring possible, and allows controlled visitor access that supports the park’s economic viability. It has produced one of the longest continuous behavioural data sets on any primate population, with researchers including Junichiro Itani and his successors having published work on the troop continuously since the 1960s.
The case against provisioning: it artificially elevates the local population above natural carrying capacity, which produces compensating stresses (higher disease transmission, intra-troop aggression, changes in dispersal patterns). It modifies the behavioural repertoire of the population in ways that may not represent natural behaviour. It creates dependency that constrains future management options. And it can mask the real-world impacts of habitat change on the broader regional macaque population.
The current management balance — substantial but not unlimited provisioning, with the population monitored closely and supplementary feeding adjusted seasonally — is a workable compromise but not a stable equilibrium. As the population ages, as the surrounding ecological context shifts, and as visitor pressure changes, the provisioning regime will likely need adjustment.
Visiting Jigokudani
The park is one of the more accessible wildlife-viewing destinations in Japan. From Tokyo, the journey takes about three hours by Shinkansen to Nagano followed by a local train to Yudanaka and a short bus or taxi to the park entrance. From the park entrance, a 1.6-kilometre walking trail leads through bamboo forest and along the river to the monkey-bathing area. The walk is moderate but icy in winter — sturdy boots are essential.
The best viewing season is late December through early March, when the snow cover is deep and the macaques use the hot springs most intensively. Mid-January is the peak. Visitor numbers can be substantial — Tess’s note: arrive at opening time if you want clear sight lines for photography, and budget at least two hours at the bathing area to observe behaviour beyond the standard “monkey in the snow” shot.
The park has straightforward visitor rules that should be observed without exception: do not touch or attempt to feed the macaques, do not bring food into the viewing area, do not block the trails the monkeys use to move between the springs and the surrounding forest. The macaques are habituated to human presence but they are wild animals; bites from displaced or stressed individuals do occur and are rabies-screened as a precaution, though Japan has been free of rabies for decades.
What the Documentary Got Right
The “Monkey Hot Tub” segment is brief by documentary standards but handles the basics well. The cinematography of the bathing behaviour is strong (winter in Jigokudani is a photogenic place by any measure). The interviews with park staff and visiting researchers give the audience the cultural-transmission framing without over-explaining. The ecology is presented with appropriate restraint — the segment does not romanticise the population as living in pristine wilderness, which it isn’t.
Where the segment is weaker is in the broader context. The Jigokudani population is one of dozens of provisioned macaque populations in Japan, with similar long-term research programmes at sites including Koshima Island (where the Imo troop’s potato-washing originated), Arashiyama in Kyoto, and several others. The provisioning question — and the broader ethical and management issues of long-term wild-animal research at provisioned sites — would benefit from a longer treatment than the segment can provide.
The Broader Japanese Macaque Story
Japan has approximately 100,000-150,000 wild Japanese macaques across multiple populations, with substantial regional variation in behaviour, morphology, and cultural traditions. The species is not endangered but several local populations are under pressure from habitat fragmentation, agricultural conflict (macaques regularly raid crops in rural Japan, which has produced ongoing tension between conservation and farming interests), and the demographic shifts in rural Japan (depopulation of mountain villages has both reduced direct human pressure and changed the landscape mosaic in ways that affect macaque habitat).
The species has been studied continuously by Japanese primatologists since the 1940s. The Japan Monkey Centre at Inuyama and the various regional research stations represent one of the most sustained national primate research programmes in the world. The cumulative research output on Japanese macaques exceeds that on any other Old World monkey species.
What to Watch and Read Alongside
For viewing, our team’s recommendations: David Attenborough’s Life of Mammals includes solid Japanese macaque material. NHK World has produced multiple documentaries on the various provisioned macaque populations — the Koshima series in particular is worth tracking down. For long-form, the BBC’s Snow Monkeys (2014) is a feature-length treatment of the Jigokudani population that goes substantially deeper than the Wild Japan segment.
For reading, Frans de Waal’s The Ape and the Sushi Master includes substantial coverage of Japanese primatology and the cultural-transmission framework. Junichiro Itani’s translated essays are the foundational reading for the Japanese tradition of primate research. For the broader animal-culture question, Hal Whitehead and Luke Rendell’s The Cultural Lives of Whales and Dolphins covers parallel research in cetaceans.
Why the Soaking Macaques Matter
Geography Scout’s broader interest is in what specific cases like the Jigokudani population teach about the boundary between biological adaptation and cultural learning in animals. The case for non-human animal culture has been built across the past sixty years from a handful of very-well-documented populations, and the macaques in the hot springs are one of the foundational case studies. They are also charming, photogenic, and accessible — none of which is a substitute for the underlying science but all of which contribute to public engagement with primatology in ways academic publications cannot. Tess says the trip to Jigokudani is one of the most worthwhile wildlife experiences she’s had in Asia. Plan it for January. Bring layers.
Related Reading from Geography Scout
- World’s Weirdest: Strangest Species Documentaries — other extraordinary animal behaviours.
- Maneater Manhunt: Why Some Predators Become Human Killers — wildlife conflict and conservation.
- Blue Whale Communication: Songs Across Entire Oceans — non-human animal culture and communication.
Further Reading
