Acoustic analysis of the 'giggle' sound emitted by spotted hyenas has revealed that their laughter may encode distress signals, besides information about age, dominance and identity.
Researchers recorded the calls of 26 hyenas in captivity and found that variations in the giggles' pitch and timbre may help hyenas establish social hierarchies. It might also signal calls for help in danger.
Frederic Theunissen, from the University of California at Berkeley, and Nicolas Mathevon, Universite Jean Monnet in France, worked with a team of researchers to study the animals in a field station at Berkeley.
Theunissen and colleagues also suggest that the giggle may be a sign of frustration and that it may be intended to summon help.
He said: '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.
'The hyena's laugh (also) gives receivers cues to assess the social rank of the emitting individual. This may allow hyenas to establish feeding rights and organise their food-gathering activities,' Theunissen added.
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.
These vocalisations are mainly produced during food contests by animals that are prevented from securing access to a kill, said an UC-B release.
These findings were published in the open access journal BMC Ecology.