The surprising shade preferences of Japanese macaques
When the temperature climbs, most humans instinctively rush into the darkest corner available. The same logic would seem to apply to other warm‑blooded animals, yet a recent study on Japan’s Yakushima Island reveals that Japanese macaques—known for their dense winter coats—sometimes opt for a more nuanced thermal refuge. Rather than seeking the coolest, fully shaded spot, they often settle where part of their bodies basks in sunlight while the rest remains in shadow.
Field observations that sparked a hypothesis
Yoshiyuki Tabuse from Kyoto University began his year‑long investigation after noticing a handful of macaques perched in what appeared to be “half‑shade.” This intermediate zone had been largely ignored in thermal regulation research, which traditionally focuses on the binary choice between sun and full shade. Tabuse wondered whether a middle ground could provide a flexible means of heat exchange, especially for primates with thick pelage that traps warmth.
Methodology: tracking shade use under varying humidity
The study followed 24 adult female macaques from October 2020 to October 2021, capturing 722 distinct resting or low‑activity events on sunny days when all three microhabitats—full sun, partial shade, full shade—were accessible. Researchers quantified the proportion of each animal’s body exposed to direct sunlight: 0‑33 % classified as shade, 33‑67 % as half‑shade, and 67‑100 % as sun. Simultaneously, ambient temperature and relative humidity were recorded to assess their combined influence.
Humidity flips the shade preference
The data unveiled a clear pattern. In cooler conditions, humidity played little role, and macaques distributed themselves fairly evenly across the three zones. However, as temperatures rose, a split emerged. On hot, moist days the animals gravitated toward full shade, presumably to maximize evaporative cooling. Conversely, during hot but dry periods they favored half‑shade, exposing part of their bodies to sunlight while still obtaining some cooling relief.
This behavior suggests that partial shade offers a thermal compromise: it limits overheating while allowing limited solar warming that may aid in dissipating excess moisture or maintaining muscle temperature. The exact physiological advantage remains unknown, and Tabuse plans follow‑up experiments to isolate the mechanisms.
Broader significance amid climate change
The findings underscore that humidity, not just temperature, can reshape animal behavior. Many heat‑stress studies overlook moisture, focusing solely on thermoregulation. As climate change drives higher temperatures and alters precipitation patterns, the ability of wildlife to fine‑tune microhabitat use could become a critical survival strategy.
Japanese macaques, the most northerly non‑human primates, provide a valuable model for understanding how mammals with dense fur cope with warming environments without migrating. Their seemingly simple choice of a resting spot reveals a sophisticated balance between solar gain and cooling, a balance that could inform conservation practices aimed at preserving suitable microclimates within fragmented habitats.
In summary, the study challenges the assumption that animals always seek the coolest possible refuge when it gets hot. Instead, it highlights a flexible, humidity‑dependent strategy that may prove essential as the planet continues to warm.
Source: https://scientias.nl/japanse-makaken-zoeken-tijdens-een-warme-dag-niet-altijd-de-koelste-plek-op/
