Marine Mammals Listen to Orca's

[Madame Butterfly 0]

Marine Mammals Eavesdrop on Orcas

By Jennifer Viegas, Discovery News

Nov. 12, 2004 — When killer whales sound off, mammals listen, according to a recent study that found seals, sea lions, dolphins, porpoises and other marine mammals eavesdrop on the killer whales that like to eat them.

 

The study suggests some animals pay attention to other animals communicating when it is in their best interests to listen to the enemy. It also reveals how call patterns of animals can co-evolve because of eavesdropping.

 

 

“ When we played calls of transients, the seals disappeared under water and moved toward shallow areas and patches of seaweed where they would be safe from killer whales.

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Marine biologists conducted the extensive study from 1999-2003 in Johnstone and Queen Charlotte Straits, British Columbia, and in Glacier Bay, Icy Strait and Stephens Passage, southeastern Alaska. From a boat or from an elevated point on shore, the scientists used binoculars to locate transient and killer whales and then followed them by boat. An underwater microphone called a hydrophone picked up the whale calls.

 

The findings are published in the current journal Animal Behavior.

 

Although the two types of whales are from the same species, Orcinus orca, they have very different lifestyles. According to the research, resident killer whales live in large, stable groups and feed only on fish, especially Pacific salmon.

 

Transient killer whales live in less tightly structured groups and exclusively hunt warm-blooded prey, which include harbor seals, Steller and California sea lions, harbor and Dall's porpoises, Pacific white-sided dolphins and an occasional seabird snack.

 

The scientists who listened in on the resident and transient whales paid attention to the killer whales' vocalizations before, during and after hunting, which often could be heard on the hydrophone because the whales munched and crunched with great gusto.

 

Overall, the scientists found that residents were a much chattier group. They produced .34 calls per minute versus .05 calls per minute for transients.

 

Many transients went silent just before a hunt, but then became quite communicative after they killed their prey and seemed to want to share food with other transients. The researchers theorize this is because marine mammals have a keen sense of hearing and can eavesdrop on the transients.

 

Salmon, in contrast, have poor hearing, so the scientists indicate the residents would not improve their hunting skills by curbing their calling.

 

Volker Deecke, lead author of the paper and a biologist at the University of British Columbia, as well as a researcher at the Cetacean Research Lab in Vancouver, conducted another study that further supports the claim that killer whale prey listens to transients.

 

"When we played calls of transients, the seals disappeared under water and moved toward shallow areas and patches of seaweed where they would be safe from killer whales," Deecke told Discovery News. "When we played calls of familiar killer whales (residents), the seals could not have cared less — they stuck around and, if anything, moved a little closer to our loudspeaker."

 

The findings could suggest marine mammals translate what the whales are saying, but Deecke has doubts.

 

"This doesn't necessarily mean that the seals understand what the killer whales are communicating, but it does prove that their acoustic perception is sophisticated enough to allow them to distinguish between the calls of harmless and dangerous killer whales," he said.

 

Deecke, however, did add that studies on other animals have shown Dr. Dolittle-type abilities exist among different species. He said forest monkeys can decipher the alarm call of another monkey species, and hornbills, a tropical forest bird, can decipher monkey and eagle alarm calls.

 

Patrick Miller, a Royal Society International Fellow at the Sea Mammal Research Unit at the University of Saint Andrews in Scotland and an expert on killer whales, agreed with the recent findings.

 

"I think Volker's work documenting the calling behavior of transient killer whales is an important contribution to our understanding of this fascinating animal," Miller told Discovery News.

 

He indicated that eavesdropping saves the seals from living a life on the run.

 

"The seals are able to tell apart the calls of the resident and transient whales, which is important because the fish-eating whales call a lot of the time and the seals could waste a lot of time reacting to non-threatening sounds," Miller said.