New Technology Reveals Killer Whale Conversations
A new technology is allowing scientists to eavesdrop on the deep conversations of killer whales. For the first time they can not only listen in on a group of whales, but now they can decipher which one is doing the talking.
Killer whales (Orcinus orca) live in stable families. The kids stay with their mother for their entire life. As many as four generations of whales live together in some of these matrilineal groups.
Within these families, members are incredibly vocal. But most research to date has used underwater microphones, called hydrophones, to study the collection of sounds produced by various groups—not individuals.
"This is like using a microphone at a cocktail party—you can't see or hear who said which thing," said Patrick Miller, a marine biologist at the Natural Environment Research Council Sea Mammal Research Unit at the University of St. Andrews in Fife, United Kingdom. Miller led the research that will be published in the journal Animal Behavior.
Not knowing which whale said what makes it difficult to interpret orca, or killer whale, communication and social bonds.
Marine mammals are often very difficult to observe during research, so it is almost impossible to ascribe sounds to individuals in these tight-knit matrilines. Miller and his colleagues developed an instrument and technique that allows researchers to assign calls to individual killer whales. "That's never been done before," Miller said.
Look Who's Talking
As killer whales feast on salmon in the waters of Johnstone Strait—sandwiched between the northeast coast of Vancouver Island and the rugged, snowy peaks of the mainland—they holler back and forth, precisely repeating each others' calls. Many times the same call is echoed over and over as the two individuals continue to call and respond.
Miller and his colleagues dragged a hydrophone array—a string of hydrophones—behind the research vessel, conducting "sound traces" to determine the angle at which certain calls originated. With laser range finders and a compass, Miller matched the calls with visual data to pinpoint a particular animal. The method works well when the animals are separated by greater than about 115 feet (35 meters).
Canadian researchers, led by the late Michael Biggs, laid the groundwork for these studies. They spent the last several decades photographing the fins of killer whales and produced a catalog of the members of groups within the British Columbia/Washington State region. Miller and his colleagues used these catalogs to identify whales based on their unique fin shape and pattern.
"It shows what sophisticated techniques are required to monitor these conversations," said Volker Deecke, a marine biologist at the Marine Mammal Research Unit at the University of British Columbia in Vancouver, Canada. Deecke studies vocal behavior in transient killer whales, which tend to have a larger range and different diet from Millers' resident fish-eating orcas.
Window Into Orca Culture
Killer whales bunch together when they socialize or rest—touching, rubbing, resting, and rolling on the surface. They spread out to find food. But even when they separate they remain in acoustic range.
There are between 7 and 17 calls in the repertoire of the average killer whale matriline. However, during the dialogues that Miller recorded, the call produced by the first individual was copied almost immediately by the responder—a phenomenon that the scientists dubbed "call-matching."
At one point they noted such an exchange between a mother and calf.
But it is not yet clear what these exchanges mean. It could signal that the responder is aware of the first caller and is paying attention, or that the message might simply have been received.
"Call-matching has been found in a number of species, and probably has a variety of meanings," Deecke said.
In primates, call-matching can be used as a sign of reconciliation after a nasty situation or fight. In some songbirds, song-matching signals a "stay away" territorial warning.
"Miller's work is the first step to understanding the function of these calls in the context of killer whale behavior," Deecke said.
The fact that call-matching behavior is seen in other species suggests there might be basic rules of communication, Miller said. He intends to follow the call-matching observations with underwater playback experiments to see how killer whales respond to a range of calls.
The ability to identify individual callers and calls also provides an opportunity to study how vocalizations are passed from one generation to the next, opening a window into killer whale culture. Now the trick is to figure out what these creatures are saying.
Fuente:National Geographic News