Yes, it has its naysayers, but Wikipedia is an amazing repository of odd and little known facts to amaze and delight the perpetually curious. For instance, apparently there is a mythical African tribe called the Bouda comprised of "werehyenas," i.e., able to transform into hyenas. A similar notion can be found in the folklore of the Bornu tribe in Nigeria; they even have a specific word that translates, "I change myself into a hyena" (bultungin).
Perhaps such myths endure because the spotted hyena (Crocuta crocuta) in particular has a very rich repertoire of sound the use when communicating with each other. Hyenas have a bit of a bad rap as low-life scavengers — a trio of them were villains in The Lion King, in fact, whose high-pitched shrieking maniacal laughter gave my 8-year-old niece nightmares. But in fact, they hunt and kill most of their prey, usually by cooperating with each other in the hunt. Hyenas are very complex social animals, living in large clans, each dominated by an alpha-female. Go, matriarchy!
And like any organized society, a certain number of rules have evolved to govern the pack interactions. Quarrels are rare and easily resolved with a few loud noises and a couple of well-placed nits. There's a certain amount of socially acceptable grooming between mothers and cubs, and like most canine pack animals, the standard greeting involves lots of sniffing and careful inspection of the genitalia, although Wikipedia notes that "adult males rarely greet with females in this matter." (Quel turnoff!) Males rank dead last in the social hierarchy. So male hyenas tend to be smaller and less aggressive. Interestingly, the calmer and more docile males are preferred as mates, rather than the more aggressive ones. They tend to be patient, too, since the females will let the courtship drag for as long as a year before succumbing.
Such a complicated social structure requires a fairly sophisticated communication system. We've already mentioned the giggling: that high-pithed cackling laugh that freaked out my young niece. Ironically, it appears to be a sound associated with intense fear, since it's usually emitted by hyenas who are being chased by predators. There's also yelling — more of a roaring scream emitted by hyenas seeking to evade attackers.
Lowing indicates impatience ("It's my turn to feast on the kill!"), while the whoop is more of a contact call. It can vary in pitch and intensity, but a fast whoop seems to be rallying cry during a kill or other type of conflict. And each hyena has its own unique trademark whoop used for identification purposes. The most common sound hyenas make is the groan, but there are several different types, ranging from a low growling noise to softer, more tonal sounds used when greeting. Bioacousticians have classified them into different groups, based on acoustical characteristics of the various groans. It seems the hyenas can modulate the sounds they make depending on the behavioral contexts.
We tend to associate hyenas with giggling — the laughing hyena — but it seems that a hyena's giggle might be less telling than its groan. Researchers at the University of California, Berkeley, have studied the acoustic properties of the various "vocalizations" of the spotted hyena. They find that the giggle is used more frequently in competitive situations — haggling over prey, shooting hoops on the Savannah — while loud whooping calls are used more for long-distance communication.
Hyena groans were the focus of UCB's Frederic Theunissen's talk last week at Acoustics '08 in Paris. To decipher the meaning of these vocal signals, Theunissen and two colleagues — Suzanne Page and Steve Glickman — presented adult hyenas with three different objects: unfamiliar spotted hyena cubs (who might not have enjoyed being thus objectified), big meaty bones, and an empty transport cage in which bones or cubs had been housed on other experiments. The results: the cubs elicited more groans from more hyenas than any of the other objects, and those groans had a lower fundamental frequency, and were less "tonal" than the groans produced in response to the bones or empty cage. (You can hear sound samples of the vocalizations here.)
Theunissen acknowledges that the exact meaning of the specific types of groans isn't quite clear; it's not like they can ask the animals, "So, what did you mean by that?" And so far they on;y have a limited number of recordings of the vocalizations — not enough to draw many definitive conclusions. One might assume that the groans directed at the cubs would be friendly, particularly from female hyenas, except in this case the cubs were unrelated. The groans might have been a warning signal instead. (I guess it depends on how hyenas feel about adoption — and as an adopted child, I can joke about that.) Per Theunissen:
It is possible that the lower pitch and less musical growls produced to the meaty bone signal a more aggressive approach ("that bone is mine") while the more tonal and higher pitch groan signal signifies a friendly approach ("it is ok little cub"). But given that our cubs were unrelated to the subjects in the experiment, and that deception is also a possibility ("it is okay little but I might kill you"), we have to be careful when we attempt to associate a meaning to the sounds.
Theunissen's team also studies the groans elicited by mother hyenas to their own cub in the same situation, which turned out to be more tonal and of higher pitch than those used toward an unfamiliar cub. More studies are being planned. Offhand, I'd have to agree with Theunissen when he says, "Human language might be unique in its complexity and flexibility, but hyena vocalizations are more telling than any of us could imagine."