Dolphins May Eavesdrop on Each Other, Study Suggests

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Steve Dawson is a marine mammal researcher at the University of Otago in New Zealand who was not involved in the study. He also thinks eavesdropping is the most likely explanation for the findings.

Dawson says the theory would explain why dolphins have not evolved to use language beyond a simple range of sounds to communicate with others in a pod, despite their relatively large brains.

For dolphins, echolocation "can carry all sorts of complex information about whether a dolphin is pregnant, what mood it's in, and what's around it," he said.

Listening in to each other's mapping and foraging efforts would make group communication even easier.

"In essence, if you were to sense a fish, you wouldn't need to tell me there's fish over there, because I would already know," Dawson said.

Dawson adds that the animals' ability to eavesdrop may have contributed to the evolution of cooperative behavior in dolphins.

Acting selfishly would be harder, he said, because others in the group would "be in on whatever you might try to get away with."

Enough Evidence?

Götz's findings are not the first evidence that dolphins can understand each other's echolocation signals.

Previous research on captive Atlantic bottlenose dolphins (Tursiops truncatus) demonstrated that they are capable of deciphering the echoes from another individual's clicks.

The 1996 study showed that a dolphin could correctly identify objects without seeing them or using echolocation. The animal simply listened to another dolphin's echolocation signals as it was presented with an item.

Like dolphins, bats also use echolocation to assess their surroundings.

For example, when a bat approaches an insect, it speeds up the repetition rate of its signals to get a better reading on its prey. The change indirectly alerts other bats to the snatch, says Hans-Ulrich Schnitzler, Götz's supervisor and study co-author.

"But we don't have the situation where one bat emits a signal and all others are waiting for the returning echo," Schnitzler said. "[Bats] can tell if something's going on, but dolphins truly eavesdrop."

Götz, however, admits that his data, detailed online last month in the British science journal Biology Letters, does not definitively prove the theory.

Whitlow Au, chief scientist for the Marine Mammal Research Program at the University of Hawaii, is also not convinced the wild rough-toothed dolphins were necessarily eavesdropping.

"I think it's questionable whether the evidence is strong enough," he said.

"But understanding how marine animals do things in the wild is extremely difficult."

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