A wild bottlenose dolphin answers when it hears another dolphin mimic its individual signature whistle, just as a person responds when someone calls his or her name in a crowd, animal communications experts at Scotland’s University of St. Andrews reported Monday.
The research offers new evidence that bottlenose dolphins can learn each other’s whistles and respond to their own signature calls in a way that mirrors how humans learn and use each other’s names, experts said. That makes these gregarious sea creatures unique among nonhuman mammals, the researchers reported in the Proceedings of the National Academy of Sciences.
“We show that they really react,” said dolphin researcher Vincent M. Janik at St. Andrews, who conducted the experiments with colleague Stephanie L. King. “They turn around. We even had some animals stop and come to the boat.”
Swimming through the seas, the bottlenoses, the most common type of dolphin, regularly produce underwater arias of high-frequency moans, trills, grunts and squeaks to help them navigate and hunt.
In the 1960s, marine biologists discovered that captive dolphins produced individualized whistles. Ever since, they have puzzled over how these social animals—whose brains are second only to humans in relation to body size—might use such musical riffs to communicate in the wild.
Dolphins are among the few species that can make up new sounds to label things they encounter. They start developing their own signature identification calls when they are just a few months old, researchers determined.
Earlier this year, Dr. Janik and his colleagues reported that wild bottlenose dolphins readily learned and repeated the signature whistles belonging to close relatives and companions. But until now, no one knew whether or not these dolphins answered to their individual calls.
On Monday, Dr. Janik and his colleagues reported the results of experiments they conducted among a dozen groups of wild bottlenose dolphins, totaling about 150 dolphins in all, off the east coast of Scotland during both 2001 and 2010.
To see if these dolphins responded to a call, the researchers recorded a single signature whistle coming from a group of free-swimming dolphins. They then replayed the recording as well as a computer synthesis of the modulated frequencies that the whistle contained.
Among each group, a single dolphin responded to its individual call in eight out of 12 playbacks, usually within a minute, the researchers reported. The creature answered the call by repeating its identifying whistle.
“We found that the animal calls back only when it hears own signature whistle, or a computer version of it,” Dr. Janik said. “This shows us the animals can be addressed by using their signature whistles.”
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