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Lemurs seem to hug trees to keep cool on sweltering days.

, affiliated with Yale University, and her colleagues noticed that in the Bez脿 Mahafaly Special Reserve in south-west Madagascar, a type of lemur called the white sifaka (Propithecus verreauxi) hugs the base of tree trunks on particularly hot days.

鈥淲hen we first saw it, it was just so unusual because these are highly arboreal [tree-dwelling] primates,鈥� she says.

With sifakas having fewer sweat glands than most primates, the researchers wondered if hugging the trees helped the animals regulate their body temperature amid intense heat.

To learn more, the team watched six groups of sifakas during the hotter part of Madagascar鈥檚 dry season, noting tree-hugging habits over a total of 615 hours. During these observations, the researchers also logged the temperature of the air, ground and trees at several heights.

Over two months, they noted 64 episodes of tree-hugging by 20 sifakas in five of the six groups. The embraces lasted from around 1 minute to more than 4 hours.

Hugging only took place when air temperatures rose above 30掳C. Each 1掳C increase beyond this doubled the chance the lemurs would hug trees.

The bases of the hugged trees were roughly 3掳C to 5掳C cooler than both the higher parts of the trees and the surrounding air, suggesting that the lemurs embraced the bottom of the trunks to release some heat.

The three most frequently hugged tree species 鈥� Salvadora angustifolia, Syregada chauvetiae and those belonging to the Olax genus 鈥� had more than a 4掳C difference between the temperature of the air and that of the tree base, on average.

This is potentially a very effective way for these lemurs to lose heat without relying on evaporative cooling, says Natalie Briscoe at the University of Melbourne, Australia, who observed similar behaviour in koalas.

Studying the lemurs鈥� preferred trees more closely could help with conservation efforts in the face of predicted warming, says Chen-Kraus.

Some of the sifakas 鈥� particularly the smaller and younger ones 鈥� also entered the hollow trunks of S. angustifolia on hot days, where it could be more than 10掳C cooler than outside.

But more frequent hugging could also spell danger, says at the Pontifical Catholic University of Rio Grande do Sul in Brazil. 鈥淎n increase in the frequency of this behaviour will impose more serious risks of predation.鈥�