A kind word or gesture from a friend can give you the warm fuzzies. But a warm, fuzzy friend can give a macaque a better chance of surviving the winter. After following dozens of macaques through snowy woods for months, scientists found that friendlier monkeys earned themselves more cuddle buddies on cold nights.

Earlier studies in macaques, baboons and even wild horses have shown that animals who are more social may live longer and have more offspring. In other words, “friends with benefits” is no joke in the animal world. Liz Campbell of the University of Lincoln in the United Kingdom and her colleagues wondered if they could find a mechanism that makes friendship so beneficial. They started looking in the mountains of Morocco.

From January to April 2015, the researchers followed two groups of Barbary macaques (Macaca sylvanus) through the woods. These monkeys are used to cold conditions; there was snow on the ground continuously for three of the four months of the study. At night the macaques sleep in tree branches, often huddled together for warmth.

The scientists wanted to know what factors affected the number of nighttime cuddle buddies a macaque had. They didn’t do anything to the monkeys except watch them—from 6:00 AM to 7:00 PM every day. Researchers followed macaque groups to the sleeping site they picked out each evening, then returned before sunrise to record who was huddled up with whom before the macaques awoke.

The macaques slept alone or in cuddle piles of up to four, not counting babies. (The size of a huddle—or “social thermoregulation aggregation,” as the scientists call it—is limited by having to fit on a tree branch.) The researchers found that in colder, wetter weather, the monkey huddles were larger. This confirmed that macaques use nighttime cuddling to fight off the chill. The researcher also saw that if two macaques hung out and groomed each other during the day, they were more likely to huddle together at night. And they saw that monkeys who had more grooming partners also slept in bigger huddles.

But a macaque’s social rank didn’t affect its huddle size. Neither did being male or female. The only thing that mattered was how many friends the macaque had made through grooming.

In an earlier study, researchers had found that Barbary macaques with more social relationships were more likely to survive an especially harsh winter. The new study shows why: those friends become one big blanket at night. But the authors say huddling could also be helpful for animals that live in milder climates. The other birds, mammals and reptiles that huddle for warmth during cool nights or rainy days could also get a fitness advantage. Perhaps for these species, too, friendlier individuals fare best.

Photo: Michelle Bender (via Flickr)