As the only lemur that sings, the eerie sonorous calls of the indris echo through the rainforests of Madagascar in which they survive. The whooping songs are sung by breeding pairs of the primates as a way to tell any other indris in the areas that this is their patch and that they’d better watch out. But it turns out that adolescent indris go rogue.

In a study looking into the rhythm, timing, and pitch of the indris’ singing, researchers have found that while the dominant pair sing in sync with each other, young indris looking to make a break with the family group will sing in antiphony, or asynchronously with their relatives. The scientists think that this might be a way for the primates to stand out from the crowd and make a name for themselves to any other groups of indris who might happen to be listening in, including any potential mates.

“Synchronized singing produces louder songs, and this may help to defend the group's territory from rival groups,” explains Giovanna Bonadonna, who co-authored the paper published in Frontiers in Neuroscience. “Singing is interpreted as a kind of investment, which may help to provide conspecifics with information on the strength of the pair bond and the presence of potential partners.” To combat this drowning out, the young lower ranking lemurs sing out of sync, advertising their individuality.

Indris are the largest living species of lemur, and, like all others, is limited to the island of Madagascar. The strange-looking, critically endangered primates with piercing greenish-blue eyes climb and leap from tree to tree, holding their body upright. Their ghostly songs fill the forests, and as one of the few primate species that sing, the researchers were interested in whether the songs followed a set pattern and if they had rhythm.

"Indris are indeed good candidates for further investigations into the evolution of vocal communication," says Professor Cristina Giacoma from the Department of Life Sciences and Systems Biology, the study's final author.

^{The primates live in family groups, dominated by the breeding pair who are largely monogamous. nomis-simon/Flickr CC BY 2.0}

Sequences of rhythm are central to the core of the musical melodies that most of us listen to on a daily basis, but where our ability to produce such sounds originated has remained an open question. Have humans carried such an ability from before the time that we descended from the trees, or did we somehow acquire it in our more recent past?

Rhythmic sounds are common in other apes, as “drumming” has been observed in chimps, bonobos, and gorillas both in the wild and in captivity. But just because they can produce these sounds, doesn’t necessarily mean that they know what they’re doing. It has long been suggested that monkeys can’t perceive a beat and so cannot coordinate their movement with it.

^{Main image: Brian Gratwicke/Flickr CC BY 2.0}