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A team led by Frédéric Theunissen, from the University of California at Berkeley, and Nicolas Mathevon, from the Université Jean Monnet at St. Etienne, France, recorded the calls of 26 hyenas (Crocuta crocuta) in captivity in a field station at Berkeley. They found that variations in the giggles' pitch and timbre may help hyenas to establish social hierarchies, they reported this week in the open-access journal BMC Ecology.

Said Theunissen: "The hyena's laugh (listen here) gives receivers cues to assess the social rank of the emitting individual. This may allow hyenas to establish feeding rights and organize their food-gathering activities."

The researchers found that while the pitch of the giggle reveals a hyena's age, variations in the frequency of notes can encode information about dominant and subordinate status, BioMed Central, publisher of BMC Ecology said. "These vocalizations are mainly produced during food contests by animals that are prevented from securing access to a kill, and have been considered a gesture of submission," BioMed explained in a news statement.

"Theunissen and colleagues also suggest that the giggle may be a sign of frustration and that it may be intended to summon help," BioMed added.

"Lions often eat prey previously killed by hyenas. A solitary hyena has no chance when confronted by a lion, whereas a hyena group often can 'mob' one or two lions and get their food back. Giggles could therefore allow the recruitment of allies. Cooperation and competition are everyday components of a hyena's life," Theunissen said.

"When hearing a giggling individual, clan-mate hyenas could receive information about who is getting frustrated (in terms of individual identity, age, status) and decide to join the giggler, or conversely to ignore it or move away."

The researchers plan to further test these hypotheses with playback experiments in the field. By: blogs.nationalgeographic.com