Many animals are capable of sensing rhythm — parrots, elephants, sea lions, chimpanzees, as reported by Current Biology. To rhythmic sounds, they can bow, step, wave their paws or hands, nod their heads, and so on. However, perceiving external rhythm is one thing, and creating rhythmic sounds independently is quite another. It was previously believed that only two species of living beings could sing rhythmically — humans and nightingales. Researchers from the University of Turin and the Max Planck Institute for Psycholinguistics have added indri lemurs to this list.
Indri are the largest representatives of lemurs, residing in Madagascar. They live in small family groups in their forest territories. Indri mark their territories with loud morning songs that can be heard from several kilometers away: first, a prolonged howling sound is heard, followed by a shorter descending phrase after a pause. Indri ensembles are well-coordinated, and their collective singing helps them not only assert their territorial rights to neighbors but also strengthen social bonds within the family. For many years, researchers have recorded the songs of twenty indri families, totaling thirty-nine lemurs. The songs were analyzed by sound spectrums, determining the beginning and end of each sound. It was found that indri are capable of maintaining a strict rhythm, where the intervals between sounds have the same duration, or when the next interval is twice as long as the previous one. The tempo of indri can gradually slow down; males and females sing at different tempos but in the same rhythm. This adherence to the duration of intervals between sounds is characteristic of the singing of humans and nightingales; in humans, such interval structure is present in the music of various cultures. Indri have become the first mammals, besides humans, to possess a sense of rhythm; it is possible that their songs contain other features that bring them closer to human music.
