Why Do We Duet? 'Aggressive Audio Warfare' (and Sonny And Cher)
By Matthew Brown | September 4th 2008 10:00 PM | Print | E-mail
If you can’t help but sing your heart out with your best friend when you hear Aladdin's A Whole New World or Johnny Cash and June Carter’s Jackson, maybe you can learn a thing or two about duets from birds. Vocal duets in the animal kingdom have long been known to occur in animals like birds, primates, and whales. But despite much research, the answer to why animals duet has been elusive and controversial. Research by Dr. Daniel Mennill, an Associate Professor at the University of Windsor in Ontario, is helping to change that with some pretty technical equipment, one duet at a time. Daniel Mennill studying duetting wrens in the humid Santa Rosa forests of Costa Rica. Photo Credit: Dale Morris. Behavioral ecologists say that bird duets are one of the most complex vocal performances of all animals--humans included. When you’re belting out an off-key karaoke rendition of Grease’s Summer Nights, don't feel bad: for tropical birds, vocal duets are sometimes so highly coordinated that human listeners mistake them for a solo. In fact, Dr. Mennill explained to ScientificBlogging that what certain birds are doing with their coordinated duets would put a choir at the Met to shame. These birds are coordinating their songs faster than humans can even think about singing. (Hear one of Mennill's recordings of duetting wrens). There have been many competing hypotheses to explain the function of vocal duetting in animals; for example, it has been suggested that duets, like the game ‘Marco Polo,’ allow partners to maintain contact when they can’t see each other. Or that duets allow pairs to cooperatively defend their mating territories. More simply, it’s been hypothesized that duetting might be a bonding experience that helps to solidify and maintain a relationship. Could it be that animals simply do it just to have fun? “Animal behaviorists tend to shy away from the question of whether or not an animal is enjoying what they’re doing,” says Dr. Mennill, "but we do notice some behavior that isn't too far removed from the idea of fun, or singing for song’s sake.” “One of the things that strikes me is that the songs are really quite beautiful. My results are the first to show that they are singing these beautiful songs more often when they are near their nest, and they are doing these as a couple, perhaps to reinforce to each other that they are in a partnership. As they establish their partnership, they sing songs like crazy! So maybe they're having fun too." The exact evolutionary significance of duets remains elusive, but today, research that will be published my Mennill's team in the September 9th print edition of the journal Current Biology gives new insight into the motivating factors that drive breeding pairs to sing duets—at least with birds. The team used sophisticated sound recording technology that allowed them to triangulate the positions of breeding pairs of birds in the dense tropical forests of Costa Rica, where the tropical wren lives. The technology can even distinguish the separate locations of the male and the female birds based on the intricacies of the slightly varied pitches and durations between male and female birds' songs. Dr. Mennill setting up the audio system in the Santa Rosa Forest. Photo Credit: Dale Morris. They found that duets produced in a natural, unprovoked context do in fact serve an important 'Marco Polo' function and perhaps a pair bonding function. But recordings of duets in an aggressive, confrontational context revealed that duets are involved in territory defense and perhaps in mate guarding. "Your first impression after you hear the duet of a pair of tropical birds is one of great harmony and cooperation," said Dr. Mennill. "Their duets require coordination and synchronization, and my multi-microphone recordings confirm that birds do coordinate their activities by performing duets. But there is a darker side to duetting; tropical birds also perform duets in very aggressive contexts, and respond with special aggression to rival individuals of the same sex. Their voices are beautiful harmonies, but they're also aggressive audio warfare." Duet function seems to vary with the circumstances, serving distinct functions in aggressive and non-aggressive contexts. During confrontations with rivals, the wrens essentially duel one another with their duets. And when they can’t find each other, one bird sings, listens for the song of its partner, and moves towards their partner after hearing a response. Sometimes the birds are as far apart as a football field, but on average they perform their duets about 20 meters apart, which is further than you can see in the dense Santa Rosa forest. It’s a way to keep tabs on their partner’s position. Close-up of a singing wren in Costa Rica. Photo Credit: Dale Morris. Mennill said he expects that, like the wrens he studied, the songs of many other duetting species also serve different purposes depending on the context in which they are performed. But he is careful to point out that duetting is very diverse from species to species, and thus we can’t exactly assume that the explanations given for wrens would completely explain the adaptive significance of the vocal duets of different animals. An important area of future research is how parents teach songs to their young. Mennill told ScientificBlogging, "My guess--and this is only a guess--is that females learn songs from their moms, and males learn songs from their dads." And if this were the case, you may be able to trace the ancestry of a bird based on the songs they sing. "You can tell a lot about where a bird came from based on the songs that they sing," said Mennill. So next time you make a trip to the grocery store and you can’t find your mate, have a little fun: make like Sonny and Cher and belt this out as LOUDLY as you can from aisle 5: “They say we're young and we don't know We won't find out until we grow” If you hear a soft and distant, “Well I don't know if all that's true 'Cause you got me, and baby I got you,” then you're good...your mate's not lost. And you can explain to the people looking at you with awkward embarrassment that you're just solidifying and maintaining a relationship.