Dolphin Social Memories: Dolphins Remember Friends' Unique Whistles After Decades Of Separation [STUDY]
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That means dolphins have the longest verified memories in the animal kingdom. The author of the dolphin social memories study, Jason Bruck, an animal behaviorist at the University of Chicago, says that while elephants and chimpanzees may have similarly long memories, they haven't been tested yet.
Bruck got the idea for the dolphin social memories study after seeing his brother's dog for the first time in four years. Though the dog dislikes most people, it recognized Bruck after the four years, making the animal behaviorist wonder how long animals can recognize faces.
To test bottlenose dolphins' memories, Bruck and his colleagues collected thousands of dolphin whistles over a period of five years. The whistles were collected from 6 different institutions around the United States and Bermuda. The dolphins were traded among these institutions from time to time, but records were kept charting each dolphin's movement.
Bruck and his colleagues played 1,200 of their dolphin whistle recordings to 43 dolphins. Some of the calls were belonged to dolphins which the study subjects had never encountered, while others were from the dolphins they knew at some point. Some of the dolphins had been together in captivity for over 18 years, while others had only spent three months with one another.
Bruck said that while the dolphins "don't pay much attention to signature whistles of dolphins they don't know," whistles from familiar dolphins elicit strong responses. "They will hover around it, whistle at it, seemingly try to get a response," Bruck said.
One female dolphin, Bailey, hadn't lived with her another female dolphin named Allie in 20 years. But when Bailey heard Allie's recorded whistle, she reacted noticeably.
But why might dolphins' social memories be so sharp, from an evolutionary standpoint? Bruck says that it may be an accidental byproduct of how they evolved.
"Why do they need this kind of memory? I'm not sure they do," Bruck said. "The cognitive abilities of dolphins are really well-developed, and sometimes things like this are carry-along traits. But to test whether this kind of social memory capacity is adaptive, we would need more demographic data from multiple populations in the wild to see if they experience 20-year separations."
Heidi Harley, a researcher who studies dolphins at the New College of Florida, said that Bruck's study was "interesting," but wasn't convinced that dolphins were reacting to specific dolphins they once knew. Rather, she suggested, they might be reacting to sounds that seem familiar to them.
"Is this really about the dolphins that produce these whistles, or is it just about the sounds themselves? It's a little hard to disentangle sometimes," Harley said.
Eduardo Mercado III, a psychologist at the State University of New York at Buffalo, echoed Harley's concerns.
"It is in principle possible that a dolphin could find a whistle more 'interesting' without having any awareness of why," said Mercado, who wasn't involved in Bruck's study.
The study was published in the journal Proceedings B.
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