Acoustic¹（声学的，听觉的） analysis of the 'giggle²' sound made by spotted³ hyenas⁵（土狼） has revealed that the animals' laughter encodes information about age, dominance and identity. Researchers writing in the open access journal BMC Ecology recorded the calls of 26 hyenas in captivity⁶ and found that variations in the giggles⁷' pitch（高音） and timbre⁸（音色，音质） may help hyenas to establish social hierarchies⁹（社会阶层，社会等级） . Frédéric Theunissen, from the University of California at Berkeley, USA, and Nicolas Mathevon, from the Université Jean Monnet, St. Etienne, France worked with a team of researchers to study the animals in a field station at Berkeley. Theunissen said, "The hyena⁴'s laugh 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 dominant¹⁰ and subordinate（次要的，从属的） status. 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 submission¹¹.

Theunissen and colleagues also suggest that the giggle may be a sign of frustration¹² and that it may be intended to summon help. He said, "Lions often eat prey¹³ previously¹⁴ killed by hyenas. A solitary¹⁵（孤独的） 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（征募，补充） of allies. Cooperation and competition are everyday components¹⁶ of a hyena's life. When hearing a giggling¹⁷ individual, clan-mate hyenas could receive information about who is getting frustrated¹⁸ (in terms of individual identity, age, status) and decide to join the giggler¹⁹, or conversely to ignore it or move away". The researchers plan to further test these hypotheses（假定，臆测） with playback experiments in the field.