Cotton-top tamarin monkeys have an ear for music created using their own sounds.
Non-human animals usually prefer silence to our music. However, when cotton-top tamarins heard songs based on their own calls, the diminutive, fluffy primates listened with interest to the monkey music, which even altered their moods, according to a new study.
Music therefore appears to be most effective when it is species specific, suggests the study, published in the latest Royal Society Biology Letters.
Co-author David Teie told Discovery News that "all of the previous studies on the effect of human music on animals has shown that they don't give a hoot about our music."
"Did we really think that bats would get little tears flowing up their little faces when listening to the 'Ave Maria'?" questioned Teie, a lecturer in the School of Music at the University of Maryland who is also a cellist in the National Symphony Orchestra.
He added, "Music is a human construct designed for humans. Absolutely everything about human music is based on human development and perception, from the speeds of the pulses to how high the melodies are. Every part of human music is based on human appeal."
To create music with more monkey appeal, Teie composed pieces using specific features in the tamarin calls, manipulating rising or falling pitches and the duration of various sounds. The music was inspired by sounds the tamarins make to convey one of two messages: fear and friendly affiliation.
When the music was played to seven pairs of adult cotton-top tamarins housed at the University of Wisconsin, the monkeys became more anxious and jittery when they heard the fearful monkey music. They then calmed down, and sometimes even foraged, upon hearing the affiliation-based music.
Regular human music was also played to the monkeys, which predictably showed little response, except for a very surprising, calming response to the heavy metal band Metallica.
Although birds, dolphins, whales and other animals produce what we call "songs," this study is among the first to show that a non-human animal can truly appreciate music.
"We think that the emotional communication part of music has an early history that predates humans," co-author Charles Snowdon, a University of Wisconsin professor of psychology and zoology, told Discovery News. "If music based on tamarin calls can alter their behavior, then our ancestors would have been able to use similar components of music to influence one another, and perhaps simple words to name things or to express actions."
Prior research has indicated that Neanderthals made bone flutes and could speak and sing.
Patricia McConnell, a certified animal behaviorist and an associate adjunct professor at the University of Wisconsin, who did not work on the study, thinks the research is "fascinating," particularly because "the music was customized to the monkey's own vocal system."
"We need more research like this," she told Discovery News. "This is exactly the kind of work that can help us understand how humans fit into the natural world, what we share and don't share with other animals, and how other animals perceive and respond to the world around them."
Teie has already composed music for domestic cats, based on feline communication and hearing. He also hopes to create a species-specific music project at the National Zoo that, he said, "would create music for enrichment of captive animals."
Metallica aside, monkey indifference to human music appears to mirror our own feelings about the customized monkey music.
"You should listen to a couple of the compositions and decide for yourself," Snowdon advised. "Those of us who have listened are not very moved by it and even find aspects aversive, as monkeys may find our music aversive to their ears."