Two spotted hyenas quarrel about an antelope backbone: Characteristic laughter signals that the higher-tiered animal signals its dominance in conflicts over food. Photo: Theunissen et al., BMC Ecology
With her characteristic laughs the spotted hyena reveals her age, her position in the pack and her identity. This has been discovered by US researchers who analyzed 695 vocalisations and their context in a clan of 26 hyenas. Through subtle nuances in pitch and length as well as the timbre, the predators establish and confirm their social hierarchy. The laughter also plays a role as a call for help in dangerous situations, for example, when a single pack member comes into conflict with lions. Above all, primates and birds have a pronounced ability to judge the relationships of other conspecifics by interpreting vocalizations. According to the study of the scientists around Frédéric Theunissen of the University of California at Berkeley, the spotted hyena also belongs to this group. "With her laughter, she gives an audible pack member an accurate assessment of her social status. As a result, the hyenas define their franchises when they eat or they organize their hunting activities, "explains Theunissen. The spotted hyena packs can count up to 90 members, are complex, and are led by dominant females.

A group of 14 females and 12 males was examined at the field research station of the University in Berkeley. The country of origin of the animals is Kenya. Over four days, the vocal repertoire of the individual clan members was first recorded in various situations, such as feeding. On the basis of this precise analysis, the individuals could be judged in their behavior in the pack. The statistical analysis considered 13 different criteria. The longest sounds of the 695 recordings lasted four seconds and included 28 notes, the shortest transmission of information took place in 200 milliseconds with two different tones.

The pitch of the laugh reveals a hyena's age. Thus, the laugh of a two-year-old animal is one third higher than that of a 20-year-old. The males generally communicate via higher tones than the females. Variations in the note frequency reveal whether a member of the clan plays a dominant or subordinate role. In the timbre, a hyena defines its individuality, which has been observed so far, especially with penguins, fur seals and seagulls.

The laughter should also be a sign of frustration and be used as a cry for help. "Lions often dispute the prey of hyenas and only a whole pack can kill several lions, " explains Theunissen. With their laughter, a single Spotted Hyena summons allies. By precisely identifying the individual, the recipient of the information immediately recognizes who is in danger. "He then decides according to the criteria of age and rank, whether he comes to the rescue or ignores the call, " explains Theunissen. display

Frédéric Theunissen (University of California, Berkeley) et al .: Online Edition BMC Ecology ddp / science.de? Rochus Rademacher

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