Just as human cliques have their own language quirks, groups of killer whales have their own dialects. But that doesn't stop them from imitating one another. A new study of wild orcas shows that they mimic calls from other groups even when members of that group aren't around. The whales could have multiple uses for the imitation, such as labeling outsiders or keeping tabs on their location.
Vocal mimicry in nonhuman mammals is rare. Songbirds are famous for imitating their neighbors, an ability they use to defend their territories. Anecdotal reports suggest that orcas mimic, too, which makes sense considering scientists have shown that their close cousins, bottlenose dolphins, mimic one another in captivity. But studying these animals in the wild is challenging because current technology can't pinpoint which animal is doing the calling, especially during mingling sessions when they are close together.
While analyzing how wild orcas near Vancouver Island in British Columbia, Canada, used sound when socializing, behavioral biologist Brigitte Weiß of the University of Vienna discovered a set of calls that were not a part of their normal repertoires. The calls seemed to resemble the calls of foreign groups that the original group would have mingled with to mate or cement alliances. Weiß and colleagues then categorized the calls and produced sonograms, which show the structure of the sound waves, to compare against sonograms of the originals. The study, published online 15 July in Marine Mammal Science, concludes that resident orcas mimicked the calls of foreign groups about once every 500 calls.
Among the thousands of calls orcas make each day, that's not often. But it's enough to stand out in their daily chatter, says Weiß. The sonograms were sometimes only superficially similar, whereas others were dead-on impersonations. "Mimicking another group's calls could be a way of referring to that group ... or of communicating something about that group to one's own family members," she says. It's equally possible that these calls have no function at all. "Most likely, the answer lies somewhere in between," she says.
"Being able to quantify this out in the wild is really interesting," says biologist Jessica Crance of the National Marine Mammal Laboratory in Seattle, Washington. "Most instances of vocal mimicry occur when the individuals that produce the original call are present." But because orca vocalizations are so varied and complex, figuring out why they keep imitating calls even when the native speakers are not around will be a challenge, Crance says.