Dolphins have the longest lasting social memory ever recorded for a non-human, according to new research that leaves open the possibility that dolphins possess the world's most impressive memories.
Could a dolphin's memory tie or surpass that of a person? Time will tell but, for now, we know that captive bottlenose dolphins can recognize the names of their old tank mates after being separated for more than 20 years.
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"This shows us an animal operating cognitively at a level that's very consistent with human social memory," Jason Bruck, who conducted the study and is a University of Chicago Comparative Human Development program post-doc, was quoted as saying in a press release.
"This is the kind of study you can only do with captive groups when you know how long the animals have been apart," Bruck added. "To do a similar study in the wild would be almost impossible."
The paper is published in the current issue of the Proceedings of the Royal Society B.
Dolphins have what are known as "signature whistles" that function like their individual names plus added information, such as sex, size and health status. Humans have something similar. When a person says his or her name aloud, for example, listeners may infer additional information. For example, a large man with a head cold is more likely than certain others to have a loud, deep and nasally voice. Figuring these sorts of things out among humans is not an exact science, though, as a short guy with a booming voice might prove.
At any rate, dolphins each have their own signature whistles, and other dolphins certainly pay attention to them, as Bruck determined.
He played recordings of signature whistles to dolphins that had once lived with the animals that made the calls. He also played recordings of dolphins that the listeners had never met.
Bruck found that "dolphins get bored quickly listening to signature whistles from dolphins they don't know." When they heard calls from their long-lost friends, however, the dolphins immediately perked up.
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"When they hear a dolphin they know, they often quickly approach the speaker playing the recording," Bruck explained. "At times they will hover around, whistle at it, try to get it to whistle back."
In one notable example, a female dolphin named Bailey, now aged 24, heard the signature whistle of another female named Allie, whom she had not seen in more than 20 years. The two females used to share digs at Dolphin Connection in the Florida Keys.
Bailey appeared to be thrilled to hear the recording of her old buddy, and tried to communicate back.
There is little doubt that relationships among these animals are deep and meaningful. The findings also indicate that these are highly intelligent animals capable of very complex mental processing.
Their communications are equally complex, such that Bruck and some other researchers now wonder if dolphins have their own language. The creation and possession of language has never technically been applied to any species other than humans.
"We know they use these signatures like names, but we don't know if the name stands for something in their minds the way a person's name does for us," Bruck said. "We don't know yet if the name makes a dolphin picture another dolphin in its head."
For his next round of research, Bruck said, "That's my goal - show whether the call evokes a representational mental image of that individual."