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Killer Whale Barked Like Sea Lion, Tapes Reveal

James Owen
for National Geographic News
August 24, 2006
 
A lone killer whale near a Canadian fishing village was a skilled mimic that barked just like a sea lion, a new study reveals.

Researchers say the barking calls of the killer whale, or orca, known as Luna proves killer whales can learn to produce novel sounds in the wild, a skill considered rare among mammals.

(Listen to Luna's bark and a sea lion's bark.)

But the finding is a posthumous one, as Luna, who gained celebrity after taking up residence near the village, was killed in a collision with a tugboat's propeller in March.

The accident happened in Nootka Sound on the west coast of Vancouver Island (map of British Columbia). Luna had lived there since 2001 after becoming separated from his pod as a youngster.

Researchers say an analysis of recordings of Luna's underwater calls confirms that the popular orca—which often followed boats and interacted with local residents—has left behind an important scientific legacy.

"Luna has certainly helped to increase our knowledge of how killer whales learn their extensive repertoires, which are specific to each pod or family group," said researcher Andrew Foote of the University of Durham in England.

"I hope this [study] also demonstrates some of Luna's individuality," he added.

The findings are published in the latest issue of the journal Biology Letters.

All Bark

Acoustic recordings of Luna made in the fall of 2003 and March of 2004 were found to include noises that sound like sea lion barks.

While California sea lions also live in Nootka Sound, the Luna recordings ranged to a frequency of more than 10 kilohertz—significantly higher than those documented for sea lion noises.

Additionally, the team says, these barks were interspersed with recognizable killer whale calls or echolocation clicks and occurred when no sea lions were present.

A killer whale call sounding like a bark had previously never been reported.

The team says Luna's barks are examples of vocal learning, whereby an animal is able to alter the way it makes sounds after listening to other noises.

Unequivocal evidence for vocal learning, the study authors write, "can include the production of novel sounds not found in the animal's natural repertoire."

Rare among animals, vocal learning is known in humans, dolphins, elephants, and certain species of birds.

Luna's barking was likely learned from the sea lions he was frequently seen around, Foote says.

"He was exposed to the sea lions for several weeks at a time and often interacted with them, which may have triggered the mimicry," he said.

Foote adds that tapes of the solitary killer whale revealed another type of unusual call, which may have had a human source.

"The call type apparently resembles the whistle of a local fisherman who used to whistle to Luna when he saw him."

Lonely Luna?

The study suggests that Luna also mimicked other killer whales he occasionally came across. Sound recordings link his calls to a different pod than those of the one he was born into.

Luna, which was born in 1999, may have become separated from his natal pod before he had time to learn the calls that identify it, Foote says.

"Each pod has a unique call repertoire," Foote said. "Although most calls are used by all the pods occasionally, many of the calls are predominantly used by one pod."

The study suggests that vocal learning may enable killer whales to develop and learn specific calls that help to strengthen family bonds and keep a pod together through group recognition.

A similar explanation has been proposed for other animal mimics that show evidence of vocal learning.

A study published last year in the journal Nature reported on an orphaned female elephant from a wildlife reserve in Kenya, East Africa. She mimicked the sound of rumbling traffic on a nearby highway.

Elephants "may well be able to produce unique calls, like a vocal signature, that are particular to that individual or to its family or to very closely bonded individuals," said lead researcher Joyce Poole, scientific director of the Amboseli Elephant Research Project in Kenya.

Poole says this ability may be particularly important to animals like elephants that often communicate over long distances.

Another study, which appeared last May in the journal Proceedings of the National Academy of Sciences, suggests that bottlenose dolphins use vocal learning to create distinctive whistles.

These so-called signature whistles are thought to act like names, helping bottlenose dolphins locate and identify others in their group.

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