The misfit male ring-tailed lemurs rely on two sounds: a moan to keep tabs on their group and a “hmm” sound to signal friendliness to the few other ring-tailed lemurs that will put up with them, says a study recently published in the journal Ethology.
Ring-tailed lemurs, which live almost exclusively on the African island of Madagascar, have a repertoire of nearly two dozen vocal calls. But the researchers say theirs is the first study to try decoding the hmm call in the wild.
The findings show ring-tailed lemurs display gregarious social behaviour that is much more nuanced than many researchers assume, says Laura Bolt, a primatologist at the University of Toronto and the paper’s lead author.
“They’re using the moan to keep in touch with the group in general, and they’re using the hmm vocalization to keep in touch with preferred individuals in the group,” she says.
Ring-tailed lemurs live in matriarchal social groups that can range from five to 27 animals. Among their many vocalizations, adults in these social groups use separate sounds to alert each other to flying predators like the Madagascar harrier-hawk or ground-based predators such as the cat-like fossa.
The females mate with multiple males in a group for up to a day and stagger their receptivity to males so that each enters heat on a different day.
Outside of these fleeting amorous interludes, male ring-tailed lemurs face a perilous social life. Many set out from their parents’ social group in adolescence, but they usually find that other groups aren’t quite so welcoming. They have to fight their way to the top of the male hierarchy; otherwise they are relegated to the bottom of the totem pole. Even then, they aren’t left alone.
“The females might smack them around a lot or bite them,” says Bolt.
As a result of this aggression and the occasional stink fight with male rivals, these individuals often end up hanging out at the periphery of social groups, which lowers their chance of abuse. “If the group moves, they are going to be the one kind of trailing behind,” says Bolt.
But these stragglers face an outsize chance of getting picked off by predators.
Bolt spent five months tracking different groups of ring-tailed lemurs in the forests of Madagascar in 2010. She alternated her days with distinct groups of lemurs, observing different males in a given group every half hour as they stayed put or moved through the forest.
She recorded their sounds and the context in which they made them—whether they made the noises more often when around their grooming buddies, for example, or females that tolerated their presence. All of the males made the two calling sounds, but low-ranking ones were more likely to go hmm.
Low-ranking males made more of the noises that keep them close to their social group, researchers found.
- PHOTOGRAPH BY CYRIL RUOSO, MINDEN PICTURES, NATIONAL GEOGRAPHIC CREATIVE
Targeting the more tolerant individuals in the group with hmm sounds may help the outlier males walk a delicate tightrope between being beaten by intolerant females and getting attacked by predators, according to Bolt.
Rachna Reddy, a PhD student at the University of Michigan who has also studied lemurs, says Bolt’s study is interesting because it shows how meaningful their social relationships are.
“They’re really making decisions every time they call,” Reddy says.
The research also gives a glimpse of how humans’ distant relatives may have interacted, or kept a tightly knit group.
Learning the language of lemurs, Bolt says, “can give us clues about how evolutionary pressures may have worked on early human ancestors.”