Snow Monkeys Bathe in Hot Springs to Relieve Stress Just Like We Do, Study Shows

A love of sliding into the bath to decompress after a stressful day is something humans share with their primate cousins, according to a new study into hot spring monkeys.

Researchers wanted to understand why macaques bathe at Japan's world-famous Jigokudani Monkey Park. They discovered that just like taking a dip in a hot bath is proven to help us to relax, stress hormone levels in macaques drop from a soak too.

The study sheds light on the behaviors of the world's most northerly species of non-human primates, and how they have adapted to extremely cold environments. During the winter, temperatures at the park can drop to as low as 5F (-15C).

Scientists at Kyoto University conducted their study, published in Primates, by analyzing 12 adult female macaques representative of the group's social hierarchy. During the spring birth season from April to June and winter mating season from October to December, the researchers collected fecal samples, assessing how long the primates spent in the hot springs and their subsequent behavior.

Japanese Macaques groom each other in a hot spring at a snow-covered valley in Yamanouchi town. A new study has offered an insight into why these animals take baths. Issei Kato
An infant Japanese macaque monkey bathes in the hot springs at Jigokudani-Onsen in Jigokudani, Nagano-Prefecture, Japan. A young female was the first macaque spotted in a hot spring, in the 1960s. Koichi Kamoshida/Getty Images

During the winter months and colder weeks, the monkeys were found to use the hot springs to stay warm. And high-ranking females, who were subjected to more stress, had more hot spring time than their lower-ranking counterparts.

"This unique habit of hot spring bathing by Japanese macaques illustrates how behavioral flexibility can help counter cold climate stress, with likely implications for reproduction and survival," the authors wrote.

A Japanese macaque monkey relaxes in the hot springs at Jigokudani-Onsen in Jigokudani, Nagano-Prefecture, Japan. Dominant female monkeys get more hot spring time than their lower-ranking counterparts, according to new research. Koichi Kamoshida/Getty Images
A Japanese macaque monkey and her infant bathe in the hot springs at Jigokudani-Onsen. Dominant females are subjected to more stress than other monkeys. Koichi Kamoshida/Getty Images

Macaques were first spotted bathing in the hot springs in 1963, when a young female was found at a hotel pool. Concerned that expecting guests to share hot springs with monkeys wasn't particularly hygienic, a dedicated monkey pool was later built.

"We suggest that hot spring bathing by this group of Japanese macaques is an opportunistic tradition that provides physiological benefits to the monkeys," the study said. "Despite the uniqueness of this behavior and its limited distribution, it demonstrates behavioral flexibility as an adaptive mechanism to cope with cold stress."