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Photo: Pygmy marmoset

A pygmy marmoset scales a tree in northeastern Ecuador. The tiny critter is a member of the first primate species in South America to be observed using regional vocal differences, or dialects.

Researchers think the language differences among marmoset groups could be the result of habitat variations or the need to distinguish themselves socially and attract mates, according to a January 2009 study.

Photograph courtesy Pablo Yepez

Matt Kaplan

Published December 3, 2009

The accents and dialects that add so much variety—and sometimes confusion—to everyday life are not unique to humans, and they may be more common in primates than previously thought. Researchers have found the first evidence for regional vocal differences in a South American primate, the pygmy marmoset.

Marmoset groups in Ecuador were recorded using unique vocalizations when communicating over distances up to 64 feet (20 meters).

"The variations could be linked to habitat, with different pitches and durations being useful in different densities of forest," said lead researcher Stella de la Torre, an ecologist at the Universidad San Francisco de Quito in Ecuador.

However, de la Torre suggests, it is also possible that the differences are the result of social interactions.

Sue Margulis, a primatologist at Lincoln Park Zoo in Chicago who was not in involved in the study, agrees.

"Accents help people to identify others of the same social group, and things may not be much different for marmosets," she said.

Marmosets may listen to the calls of potential mates to determine where they are from in an effort to avoid inbreeding, Margulis explained.

More Monkey Business

Pygmy marmosets are not the first mammals to be heard using dialects—similar vocal variations have been detected in other primates, such as Japanese macaques and chimpanzees.

Researchers have also recorded dialects in birds. But compared to people and birds, primates have been observed using dialects relatively infrequently.

"We wondered why non-human primates had such seemingly inflexible patterns of communication and speculated that it might merely be because we had not studied them enough," said de la Torre, who received funding for her work from the National Geographic Society's Committee for Research and Exploration. (National Geographic News is owned by the National Geographic Society.)

Previous studies on primate dialects have all taken place in Africa and Japan, so, de la Torre and her colleagues set out to explore the Americas.

The researchers observed and recorded 14 groups of marmosets in five areas of northeastern Ecuador for 1,722 hours.

Marmosets make two types of calls to maintain contact and interact socially. A trill is used when animals are no more than 32 feet (10 meters) away from one another. And a j-call tends to be used at distances between 36 and 64 feet (11 and 20 meters). (See above video.)

Individual animals were closely monitored and identified based upon size and coloration. Their calls were regularly recorded for later analysis.

De la Torre reports in the January issue of the American Journal of Primatology that even though all of the marmosets they studied were of the same species, there were significant regional differences in their trills and j-calls.

Spreading the Word

With dialects now known to exist in primates found around the world, there is the increasing likelihood that these distinct vocalizations are the rule rather than the exception, according to primatologists.

"It used to be thought that vocal dialects were limited to certain songbirds and marine mammals, such as humpback whales, and that the primates were rather 'inflexible' in their vocalizations," said Emory University primatologist Frans de Waal.

"But this study suggests at least the possibility, without proving it, that vocal traditions exist. We keep finding new evidence for cultural variation in primates and other animals—[clearly] the end is not in sight."

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