Indri lemurs use rhythm in their vocalizations, making them the only mammal besides humans known to do so. While all kinds of mammals make different sounds and calls, they lack rhythm, or the patterns and structure found in music. Researchers recently recorded the cries of indri lemurs (Indri indri) in the jungles of Madagascar. After analyzing recordings of 636 calls, they found that lemurs sing in rhythms common to human music. The team isn’t sure what benefits this singing in patterns may offer lemurs, but they think it makes it easier to gather younger lemurs and to defend their territories.