For spotted hyenas, a laugh can speak volumes about an individual.
Despite being portrayed as stupid scavengers who rely on the leftovers of lion prides, hyenas are highly intelligent and social predators. They communicate with each other through an array of whoops, yowls, grunts, screams, and giggles, and by using these calls an individual can call in help to run lions off a carcass or signal that it’s time to beat a hasty retreat if the odds don’t look as favorable. Yet there is more to a hyena call than just its message, and in a new study published in BMC Ecology a team of scientists have begun to parse what giggles say about the hyena making the call.
To investigate what hyena giggles might say about individual animals the team of scientists did not go into the field, but instead worked with a captive colony of spotted hyenas kept at the University of California, Berkeley. Just as in the wild, the individuals in this captive group formed a social hierarchy based around female dominance, and when hyenas are feeding together subordinate animals often giggle in front of my dominant clan members. This made the researchers wonder if giggles by individual hyenas contained information about their place on the social ladder, and so they recorded the giggles of individual captive hyenas to look at the acoustic structure of the calls.
The recorded giggle of one of the study hyenas, Ursa (wav file). [If it does not play in your browser, right click “save link as” and then play the wave file.]
After recording and analyzing nearly 700 hyena giggles from 17 animals (10 females, 7 males), and what the researchers found was the subordinate animals communicated with a wider array of giggle “notes” than dominant animals. In other words, their giggles were more variable in pitch and timbre, and while it was not always possible to distinguish all the individual hyenas from their giggles there were a few which produced unique notes. Overall, it appeared that each giggle at least had the potential of identifying which hyena was giving the call, their age, and their place in the dominance hierarchy.
The idea that information about individual hyenas is encoded within their giggles (and perhaps other calls, as well) has important implications for understanding how members of a hyena clan interact. Since giggles can carry over long distances, they can either be used to attract other hyenas to a particular area or be used by eavesdropping hyenas to know when something is up. More than that, the giggle might tell listening hyenas who was doing the giggling and where that animal stood in the social hierarchy, and this information could influence their reaction to the call. At the moment the way in which hyenas might use giggles requires more research to fully understand, but if the new study is correct the little laughs are social tools essential to navigating the complex social world of hyenas.
Nicolas Mathevon1, Aaron Koralek, Mary Weldele, Stephen E Glickman, Fr√©d√©ric Theunissen (2010). What the hyena’s laugh tells: Sex, age, dominance and individual signature in
the giggling call of Crocuta crocuta BMC Ecology, 10 (9) : 10.1186/1472-6785-10-9