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Page last updated at 01:55 GMT, Tuesday, 30 March 2010 02:55 UK
Hyena laughs and giggles decoded
By Matt Walker
Editor, Earth News

Hyenas competing over food
Hyenas scream for a share

The giggling sounds of a hyena contain important information about the animal's status, say scientists.

In the first study to decipher the hyena's so-called "laugh", they have shown that the pitch of the giggle reveals a hyena's age.

What is more, variations in the frequency of notes used when a hyena makes a noise convey information about the animal's social rank.

Details of the US-based research are published in the journal BMC Ecology.

Professor Frederic Theunissen from the University of California at Berkeley, US, and Professor Nicolas Mathevon from the Universite Jean Monnet in St Etienne, France, worked with a team of researchers to study 26 captive spotted hyenas held at a field station at Berkeley.

There they recorded the animals' calls in various social interactions, such as when the hyenas bickered over food, and established which elements of each call corresponded to other factors.

Last year, the researchers published some provisional results from the study.

Now they have confirmed that the pitch of the giggle reveals a hyena's age, while variations in the frequency of notes can encode information about dominant and subordinate status.

"The hyena's laugh gives receivers cues to assess the social rank of the emitting individual," says Professor Theunissen.

"This may allow hyenas to establish feeding rights and organise their food-gathering activities."

Spotted hyenas (Crocuta crocuta) are mainly nocturnal, living in clans of between 10 and 90 individuals.

Hyena mother with cub (Kate Shaw)
Spotted hyenas make up to 10 different types of vocalisation
"Whoops", with long inter-whoop intervals, are primarily used to signal that two individuals have become separated
"Grunts" or "soft growls" are emitted when hyenas of the same clan come into close contact

Often they hunt cooperatively, but this can generate intense competition as clan mates converge on a kill, fighting over its carcass.

However, among spotted hyenas, females dominate, holding a higher rank than all other males, whatever their age.

Profs Theunissen and Mathevon's research suggests that the animals convey this status via their laugh or giggle, which they usually make while fighting over food.

Previously their sounds had been considered a simple gesture of submission, but the new study has allowed researchers to identify exactly which individual hyena makes each giggle, and the circumstances in which they do so.

The information contained within the giggles could be especially important for males new to a clan, as they go immediately to the bottom of the hierarchy when they arrive.

Getting to know quickly who is who may give these individuals a better chance of improving their own status.

Giggles could also allow hyenas to recruit allies, for instance when one or two hyenas are outnumbered by lions fighting over the same kill.



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