To human ears, the laughs of individual hyenas in a pack all sound the same: high-pitched and staccato, eerie and maniacal. But every hyena makes a different call that encodes information about its age and status in the pack, according to behavioral neurologists from the University of California, Berkeley and the Université de Saint-Etienne, France. They have developed a way to identify a hyena by picking out specific features of its giggle.
The hyena does not laugh when it is having a good time. Rather, field biologists have noticed that hyenas make the sound when competing for food. The giggle is a sign of frustration, a call made by a subordinate animal when dominated by one of its peers.
To find meaning in the giggle, Nicolas Mathevon and his colleagues analyzed sounds made by 17 spotted hyenas kept in captivity. They developed an algorithm that can successfully identity an individual in the pack about half the time, by looking at the timbre and quality of a single note in its giggle. "It's like telling singers apart by having them sing one note and listening to the quality of that note," says Mathevon.
Their analysis also shows that the pitch of the giggle drops for older animals, and the giggles of animals that tend to be dominant are less variable. The next step will be to play different kinds of giggles to hyenas and test how the animals respond.
The talk "The hyena's laugh as a multi-informative signal" (4pAB3) by Nicolas Mathevon will be presented at the 157th Acoustical Society of America Meeting to be held May 18-22 in Portland, Ore.
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