Kyoto, Japan -- As climate change alters the temperatures of animal habitats, it seems natural that endotherms, warm-blooded animals like us, would prefer to hang out in the shade during hot weather. The use of microhabitats in the sun and shade is an important thermoregulatory behavior that has been reported across a wide range of animal species, and researchers are becoming increasingly interested in how animals -- especially those with long lifespans -- flexibly cope with thermal stress.

Japanese macaques, sometimes colloquially called snow monkeys, reside further north than any other non-human primates, and also have the highest hair density, which may make it difficult for them to dissipate heat. While observing some macaques in the field, a researcher at Kyoto University noticed that some of them appeared to choose resting sites that were neither fully sunny, nor fully shaded.

"That observation led me to wonder whether semi-shade might play a more meaningful role in thermoregulation than previously recognized," says corresponding author Yoshiyuki Tabuse.