What’s more relaxing than a hot bath to relax in the winter? “Nothing” would surely answer the Japanese macaques (Macaca fuscata), known for bathing in hot springs.
Indeed, researchers from Kyoto University (Japan) reveal in a study published April 3, 2018 in the journal Primates that these immersions reduce the stress of the animals.
The researchers studied 12 female Japanese macaques from the Jigokudani Monkey Park during two distinct periods: from April to June when temperatures are mild, and from October to December, when the cold sets in. They collected Japanese macaques droppings to measure glucocorticoid levels, hormones released in large amounts under stress. In addition, they also studied the behavior of the colony: which animal spends the most time in the hot springs, the hierarchy of the group, who attacks who.
The first unsurprising conclusion reported by the study is that Japanese macaques use hot baths more in winter to warm themselves, which improves their survival. But the most surprising thing is that these immersions have an influence on the hormonal secretion.
“We found that the average weekly glucocorticoid rate is lower during the bathing weeks, which indicates that – as in humans — hot springs have an anti-stress effect on Japanese macaques”, explain the researchers ofthe study. The scientists also found some of the macaques had a higher of glucocorticoid in their body depending on their hierarchical position in the colony.
The fact that dominant individuals can reserve access to the water sources seems to play a role. Indeed, this privilege is particularly important because maintaining one’s position in the hierarchy is expensive; high-ranking individuals have higher glucocorticoid levels than other members of the colony. Relaxing in these hot baths allows them to relax.