Dolphins, not elephants, may have the best memories of any non-human species.
In a new study
, scientists say dolphins in captivity have shown an ability to recognize former tank mates’ whistles even after being apart from them for more than 20 years.
The study, done by researchers at the University of Chicago, shows that dolphins have the longest social memory ever recorded for non-humans. According to the study, dolphins’ skills in recognizing the whistle sounds may be better than humans' facial recognition skills because human faces change over time.
“This shows us an animal operating cognitively at a level that’s very consistent with human social memory,” said Jason Bruck, a specialist in comparative human development, who conducted the study.
His study is published in the current issue of the Proceedings of the Royal Society of London B
Bruck collected data from 53 bottlenose dolphins at six facilities that were part of a breeding consortium that kept decades of records on which dolphins had lived together.
Bruck compared the dolphins’ reactions to whistles of former tank mates with those of dolphins that were not familiar with each other. His initial studies showed that “dolphins get bored quickly listening to signature whistles from dolphins they don’t know.”
“When they hear a dolphin they know, they often quickly approach the speaker playing the recording,” Bruck said. “At times they will hover around, whistle at it, try to get it to whistle back.”
Bruck said dolphins even responded to calls they had not heard in decades.
In one notable example, Bruck played a recording of a female dolphin named Allie, who currently lives at the Brookfield Zoo, for Bailey, a female now in Bermuda.
The pair had last lived together at Dolphin Connection in the Florida Keys when Allie was two years old and Bailey was four. But 20 years and six months after their last contact, Bailey still recognized the recording of Allie’s signature whistle.
“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.”
Here's a video about the experiment: