KYOTO >> Japanese macaques, a species of monkey inhabiting Japan, reduce their stress levels in winter by bathing in onsen hot springs to warm their bodies, according to new research.

Researchers from Kyoto University’s Primate Research Institute in Inuyama tracked 12 female Japanese macaques at the Jigokudani Yaen-koen monkey park in Yamanouchi, which has an onsen spa exclusively for the monkeys.

In 2014, the researchers collected fecal samples from the monkeys in spring (April to June) and winter (October to December) and measured levels of the hormone cortisol. High levels are thought to indicate high levels of stress.

According to the researchers’ findings, the monkeys’ cortisol levels were about 20 percent lower when they bathed. In contrast, their cortisol levels were about the same in spring regardless of whether or not they bathed.

Though winter is mating season for the monkeys, researchers say their stress levels tend to rise in cold weather.

“It is likely the monkeys reduce their stress by bathing in hot springs, which increases their potential to reproduce and survive,” said researcher Rafaela Takeshita.