Tuesday, April 20, 2010

What does your laugh say about you?

Do you have a friend whose laugh can be heard from miles away? Are you able to pick one of your friends or family members out of a crowd based on their laughter? Recent research has shown that humans are not the only animal with a distinct laugh. That’s right, dear reader, a study from the University of California, Berkeley has shown that a hyena’s giggle can give clues about its age and social status. The giggles of one hyena can be extremely unique and distinct from another hyena’s giggles. In fact, many researchers say that someone familiar with the hyenas can actually tell you which hyena is giggling simply by listening.

Researchers Frederic Theunissen and Nicolas Mathevon have been studying the giggle calls of a group of spotted – also known as ‘laughing’- hyenas (Crocuta crocuta). Theunissen defines giggles as “short staccato outbursts they make when they are not getting what they want.”

Hyenas live in clans that vary from ten to ninety individuals. They can hunt on their own or they can collaborate to bring down larger prey. However, both forms of hunting cause intense competition.

Hyenas have ten different types of vocalization, including the giggle call. Hyenas giggle in response to stressful situations or to conflict. For example, a hyena will giggle when being chased away from a carcass by a larger animal or when it is fighting with another hyena over a carcass. After all, the only thing worth fighting over is food, and who wants to hand over a fresh carcass?

UC Berkeley has a colony with 26 hyenas. There were 14 adult females, 10 adult males, and 2 sub-adult males. The two sub-adult males were less than two years old when the study was conducted. The vocalizations of the hyenas are recorded during feeding time at the colony. The pitch variations in the vocalizations are then analyzed. One result of the analysis of these vocalizations is that a giggle can give clues to the age of the hyena. As a hyena ages, the pitch of the giggle goes down.

In a clan of spotted hyenas, there is a complex social system with separate male and female dominance hierarchies. Interestingly enough, males are not always dominant over females. There are examples of “hypermasculinized” females that dominate over males in the clan. Analysis of these vocalizations has shown that the giggle is not linked directly to the sex of the hyena- but instead to the social status.

Theunissen and Mathevon believe that these calls in addition to other sensory forms of communication allow for many channels of communication that supports the complex hierarchy and social system. It is not unheard of that several types of cues are used for communication. Many animals rely on sound cues in addition to chemical and visual cues. These cues can lead to information about other animals such as sex and kinship. Hyenas are no exception to this, except that the acoustic cues of the vocal calls have become very important in the social hierarchy. Subordinate hyenas have a giggle that is very different from the giggles of dominant hyenas.

Dominant hyenas have a giggle that can be described as stable and confident. On the other hand, subordinate hyenas have a giggle that is extremely variable and erratic. Think of it this way- you are in lecture and you hear the professor make a joke. The students who understand the joke laugh like there’s no tomorrow (they would be the dominant hyenas). The students who have slept the entire semester laugh quietly to themselves because they are not sure how funny the joke actually is (these people are like the subordinate hyenas). Every student in the class is now able to tell who knows the topic and who could not care less. This is exactly how a hyena clan works.

As an example, Theunissin says that the more dominant hyenas have giggles similar to “he -- he -- he -- he”. The subordinate hyenas have giggles that sound more like “he hi -- ha – he.” If you want to hear the differences yourself, follow this link to the UC Berkley News.

By listening to the vocalizations a hyena makes, other hyenas can assess a situation. Hyenas that hear the giggle then decide whether or not they should join forces with the hyena producing the vocalizations. It also can be a sign of submissiveness. The erratic giggle of a subordinate hyena may show that the subordinate hyena will act compliantly with the dominant hyena. There are countless situations in which a hyena will make decisions based on the giggle that is heard. Think of it in playground terms: wimpy kids will stay away from the bullies and the bullies will pick on the wimpy kids. Not that I’m in any way supporting bullying, it’s just a good metaphor for this hierarchy. In this case a carcass is similar to lunch money- that’s not too far of a stretch is it?

Alright, I’ll cool it with the metaphors and analogies from here on out.

The point is that the giggle calls of the spotted hyena carry information about the sender such as dominance and age. They may also allow for individual identification. Unfortunately, no one knows for sure exactly why hyenas produce giggle calls, but researchers can still hypothesize. Theunissen and Mathevon bring up many advantages of giggling in their paper; for example, giggling can rally other hyenas to a carcass which might be taken over by a lion. In addition, it is important to note that this study was carried out in captivity and therefore some bias is present. Overall, hyenas are extremely complex and interesting animals- despite the bad name that the Lion King has given them. There is a lot more work that can be done with hyenas which could lead to many discoveries and a greater understanding of social relationships and animal communication.

- Mathevon, Nicolas, Aron Koralek, Mary Weldele, Steve Glickman, and Frederic Theunissen. "What the hyena's laugh tells: Sex, age, dominance and individual signature in the giggling call of Crocuta crocuta ." BMC Ecology. 10.9 (2010). doi:
- "Giggles give clues to hyenas social status." News Center.
US Berkely News. US Berkley, 2010. Web. 20 April, 2010.