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Dolphin hear, dolphin do

Captive dolphins base their whistles on human sounds.
21 August 2002


Dolphins add dinner bell to their repertoire.
c GettyImages

Young captive dolphins mimic their trainer's whistle in their calls to other dolphins, researchers say1. The finding is some of the first evidence that animals use imitated sounds to communicate with each other.

"In developing their whistle, young dolphins are incorporating sounds they hear in their environment into their vocalization," says Peter Tyack, who studies animal behavior at the Woods Hole Oceanographic Institution, Massachusetts.

When separated from their social group, dolphins whistle in short, unique bursts to signal their location and identity. They whistle through their blowholes at frequencies almost too high for humans to hear. Their human trainers use a dog whistle to communicate with the dolphins.

The whistles of wild dolphins trill up and down, but dolphins born in captivity tend to whistle long stretches of one pitch, Tyack's team found. These stretches closely matched the dog whistle - the training signal for "come get a food reward".

Choosing to mimic this signal might not be a coincidence, Tyack says. Young calves may learn that adding the dinner bell to their call elicits a rapid response from other dolphins.

Dolphins' musical skills may become more sophisticated with age. Captive dolphins' signature whistles become more variable as they get older, notes Jennifer Miksis, another member of the Woods Hole team.

Dolphins also communicate using head jerks, teeth baring and jaw claps. "They can use incredibly subtle body language and sounds to convey very detailed information about their intentions," says Miksis.

Anyone can whistle

Zoologist Diana Reiss of Osborn Laboratories for Marine Science in New York taught dolphins sounds using an underwater keyboard that produced distinct whistles when the dolphins pushed differently shaped keys2.

All captive-born baby dolphins have relatively monotonous whistles
Diana Reiss
Osborn Laboratories
for Marine Science

"After the nineteenth time they heard the whistle associated with ball, they repeated it back," says Reiss. The dolphins repeated only the ending of the whistle at first, much as a child might repeat "nana" after hearing "banana". They also whistled when they played with balls outside keyboard sessions.

But Reiss disputes that dolphins use unique calls to identify themselves - their contact calls are all based on a rising whistle, she says. She thinks that all captive-born baby dolphins have relatively monotonous whistles, regardless of their training, that become more complex with age.

Even the oldest captive dolphin in their study, which was 35 years old, had a less variable whistle than the wild dolphin of the same age, Miksis counters. Individuals of other species, such as bats, also have signature calls, she adds.

  1. Miksis, J. L., Tyack, P. L. & Buck, J. R. Captive dolphins, Tursiops truncatus, develop signature whistles that match acoustic features of human-made model sounds. Journal of the Acoustical Society of America, 112, 728 - 739, (2002).
  2. Reiss, D. & McCowan, B. Spontaneous vocal mimicry and production by bottlenose dolphins (Tursiops truncatus): evidence for vocal learning. Journal of Comparative Psychology, 107, 301 - 312, (1993).

c Nature News Service / Macmillan Magazines Ltd 2002

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Dolphin hear, dolphin do
21 August 2002

TITLE:Dolphin hear, dolphin do
DATE:2002/08/22 21:51