Rhythm, the saying goes—you either have it, or you don’t. Humans and songbirds do, but until now, the ability to vocalize to a beat hasn’t been observed elsewhere in the animal kingdom. Scientists now say they have discovered one of the hallmarks of the skill in the fluffy, black-and-white indri lemur, a species distantly related to humans and only found in Madagascar. The study opens the door to discovering musical traits in other species, experts say, and to understanding how our own rhythmic abilities evolved.
“This is a tour-de-force of fieldwork,” says John Iversen, a cognitive scientist at the University of California, San Diego, who was not involved with the study. “[It] clearly demonstrates that the endangered indri lemurs produce songs with a hallmark of musical rhythm.”
In 2009, Snowball, a sulphur-crested cockatoo, stunned scientists and YouTube viewers alike when a video of him bobbing his head and lifting his legs to the Backstreet Boys’s song Everybody hit the internet. Other birds have also displayed musical rhythm, as have a California sea lion, Asian elephants, and chimpanzees.
Yet prior to the new study, only humans and thrush nightingales have been observed singing songs that have a rhythmical structure—that is, containing features such as a “categorical rhythm.” A rhythm is considered categorical when the intervals between sounds have precisely the same duration (a 1:1 rhythm) or doubled duration (a 1:2 rhythm)—think of Queen’s We Will Rock You, which has both 1:1 and 1:2 rhythms. The pauses or rests between the beats are the same duration in a 1:1 rhythm, or doubled in a 1:2 rhythm.
To find out whether the indri lemur (Indri indri) songs have categorical rhythm, scientists at the University of Turin and local Madagascar primate researchers recorded songs of 39 animals living in 20 groups in the Madagascar rainforest. The primates typically sing every day, beginning at about 7 a.m. The calls help solidify group and pair bonds and likely communicate territorial boundaries and the reproductive states of group members; they can be heard up to 4 kilometers away.
The lemurs begin by roaring together for several seconds. After this, only the adult pair in each group sings, first uttering a long, wailing note that can last for 5 seconds, and then emitting a shorter descending phrase. A pair’s wails form a duet by coordinating the timing of its descending notes.
The team gave its lemur recordings to Andrea Ravignani to analyze. A biomusicologist at the Max Planck Institute for Psycholinguistics, he used a technique others had developed to discover rhythmic similarities between birdsong and human music. From recordings of 346 lemur duets and choruses, Ravignani extracted 636 individual sounds uttered by the 39 adult indris, 20 females and 19 males. He turned these sounds into spectrograms—a visual representation of sound frequencies and durations—for statistical analysis.
“We isolated every syllable in each song, where it started and ended, and who it belonged to,” Ravignani explains. After plotting these on a graph, “we could see it at once: the rhythm.”
The lemurs’ songs, like those of humans and thrush nightingales, had 1:1 and 1:2 rhythmic categories, as well as a common musical feature, ritardando, a slowing down of the tempo, the team reports today in Current Biology. Male and female lemurs’ songs showed the same rhythm, but had different tempos.
For humans, music with such rhythmic beats helps us all join in; the rhythm also communicates a feeling that’s important to listeners. Our cognitive system “shapes our perception, production, and sharing of musical rhythms,” Iversen says. The scientists don’t yet know whether lemurs have a similar mental system. He adds that showing the “rhythmic structure of the sounds is important to the listeners” would help strengthen the discovery’s relevance to understanding the origins of music.
Source: Science Mag