July 7, 2008 -- Spotted hyenas are well known for their laughs, but scientists have just determined that the carnivores communicate with their cubs using the hyena version of baby talk: melodic groans.
The find highlights what a complicated vocal repertoire these very social animals possess. In addition to the laughing, each hyena has its own "whoop" sound that identifies individuals, so "whoop" in hyena speak is somewhat equivalent to a person yelling out his or her name.
"Their lifestyle requires recognizing individuals within their social groups and adjusting their behavior accordingly," co-author Steve Glickman told Discovery News.
"Communication is central to complex, flexible social organization," Glickman, a professor of psychology and integrative biology at the University of California at Berkeley, added.
For the study, presented at the Acoustics08 conference in Paris last week, Glickman and his colleagues focused on hyena groans. To elicit the sounds, the researchers presented hyenas at the Berkeley Field Station for Behavioral Research with three things: meaty bones, unfamiliar spotted hyena cubs and an empty transport cage used to contain bones or cubs during other experiments.
The adults groaned more at the cubs than the objects, with cub groans sounding much more melodic and gentle. When the animals groaned at the bones and the cage, the vocalizations were less tonal and had a lower identified frequency.
Glickman said the exact meaning behind the song-like groaning to cubs remains unknown, but in the wild "groans are used by females to call their cubs from underground burrows."
Surprisingly, to human ears, the male sounds were always higher in pitch than those made by females.
"Among spotted hyenas, females are, on average, larger than males and the deeper fundamental frequencies may simply be a function of body size," he explained.
Were it not for human activity in sub-Saharan Africa, spotted hyenas would occupy most of the plains there. As it stands, they are the most common carnivores in the Serengeti, with an unfounded reputation as a scavenger. Hyenas actually kill most of their prey, often in cooperative hunts.
Their laugh has nothing to do with a good time, but instead indicates that an individual is feeling distressed or submissive. For example, a hyena might giggle at a kill site while waiting its turn to eat and being chased off by higher-ranking members of its clan.
The cubs in the study didn't hear much giggling, but instead received an earful of sweet-sounding groans.
Kay Holekamp, a Michigan State University zoologist and a leading expert on hyenas, told Discovery News that she too has heard adult hyenas groaning at cubs.
She said "in my experience with wild hyenas, I would describe the groan as a 'come-hither, I won't hurt you' vocalization, signaling friendly intent, especially to the young cubs to whom these calls are often directed."
She believes the groans may help hyena youngsters to form social relationships by distinguishing friendly from unfriendly members of their group.
In the future, Holekamp said "it would be very useful to know whether groans are individually distinctive, whether cubs can discriminate the groans of their mothers from the groans of other adult females, and whether the groans emitted by a particular hyena differ when directed at one's own versus someone else's cubs."
The Berkeley team also hopes to further study noises produced by the cubs themselves, since the babies have their own baby talk that includes soft cooing sounds.
Related Links:
Jennifer Viegas' Blog: Born Animal
Learning How to Keep a Hyena Happy
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