Abstract
A crucial, common feature of speech and music is that they show non-random structures over time. It is an open question which of the other species share rhythmic abilities with humans, but in most cases the lack of knowledge about their behavioral displays prevents further studies. Indris are the only lemurs who sing. They produce loud howling cries that can be heard at several kilometers, in which all members of a group usually sing. We tested whether overlapping and turn-taking during the songs followed a precise pattern by analysing the temporal structure of the individuals' contribution to the song. We found that both dominants (males and females) and non-dominants influenced the onset timing one another. We have found that the dominant male and the dominant female in a group overlapped each other more frequently than they did with the non-dominants. We then focused on the temporal and frequency structure of particular phrases occurring during the song. Our results show that males and females have dimorphic inter-onset intervals during the phrases. Moreover, median frequencies of the unit emitted in the phrases also differ between the sexes, with males showing higher frequencies when compared to females. We have not found an effect of age on the temporal and spectral structure of the phrases. These results indicate that singing in indris has a high behavioral flexibility and varies according to social and individual factors. The flexible spectral structure of the phrases given during the song may underlie perceptual abilities that are relatively unknown in other non-human primates, such as the ability to recognize particular pitch patterns.
Highlights
It is an open question whether the human ability to produce and perceive sequences of rhythmic sounds arose in an early or later stage in human evolution
Most studies suggest that monkeys do not perceive a beat and they cannot synchronize their movements with it (Macaca mulatta, Zarco et al, 2009; Honing et al, 2012), a certain degree of behavioral coordination between individuals can found in the chorusing of wild chimpanzees (Fedurek et al, 2013a) and the ability of auditory synchronization has been found in captivity (Hattori et al, 2013)
We found a considerable amount of co-singing in all the songs
Summary
It is an open question whether the human ability to produce and perceive sequences of rhythmic sounds arose in an early or later stage in human evolution. Previous studies have shown that generation of rhythmic sound is common for most apes, as what has been termed as drumming (Schaller, 1963) has been found in chimpanzees (Pan troglodytes, Goodall, 1986; Nishida, 2011; Babiszewska et al, 2015), bonobos (Pan paniscus, de Waal, 1988; Kugler and Savage Rumbaugh, 2002), and gorillas (Gorilla gorilla, Schaller, 1963) These sounds can be produced either by pounding with hands and/or feet on external objects or their body and are common in both captive and wild animals (Arcadi et al, 1998, 2004). Observations of chimpanzees seeking objects with particular resonant properties and using them repeatedly to drum suggested a link between the auditory and motor systems in non-human primates (reported by Fitch, 2012)
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