Snow monkeys have become one of Japan’s most iconic animals, mainly because of their love of bathing in a hot spring. Footage of the monkeys – also known as Japanese macaques – even features in the opening few minutes from the famous documentary Baraka.
Now scientists at Kyoto University have figured out exactly why the snow monkeys of Jigokudani adore a long hot soak. They looked at twelve female adults and monitored how often they bathed during the spring birthing season from April to June and through the winter mating season from October to December.
They worked out how much time they spent in the water during the different seasons and how it affected their hormonal balance. The scientists found that the monkeys – the most northerly species of nonhuman primate in the world – enjoyed a significant stress-reduction effect from their regular baths.
The Japanese macaques were more likely to take a dip in winter when temperatures were lower, and especially during particularly cold weeks. Dominant females spent more time bathing, but were also involved in “more aggressive conflicts” meaning they used up more energy. The research showed that taking a spa reduced stress hormone levels, which could also enhance their reproductive ability.
Rafaela Takeshita of Kyoto University said: “This indicates that, as in humans, the hot spring has a stress-reducing effect in snow monkeys. “This unique habit of hot spring bathing by snow monkeys illustrates how behavioural flexibility can help counter cold-climate stress, with likely implications for reproductions and survival.”
The unusual bathing habits of the snow monkeys were first observed in 1963 when a young female was spotted in an outdoor hot spring attached to a hotel. Other Japanese macaques quickly began to follow suit and for hygienic reasons, park management built a special monkey-only hot spring. By 2003, one in every three females bathed regularly in the winter.
The study also found that the 500 people who visit every day to watch the snow monkeys had no impact on the level of stress hormones released by the animals.