Dolphins can remember their mates after 20 years of meeting them, providing evidence that they have the longest social memory among non-human species.
An elephant never forgets! Neither does a dolphin. People often state that elephants have the longest memory. However, new found evidence suggests that elephants are no match to dolphins when it comes to remembering a person or recalling an incident.
A new study conducted by researchers from University of Chicago found that dolphins have the capability of remembering their old tank mates' whistles even after a separation of 20 years. This finding provides further evidence that dolphins have sophisticated cognitive abilities, specific to only a few species like humans, chimpanzees and elephants. The study looked into data from 53 different bottlenose dolphins at six facilities.
"This shows us an animal operating cognitively at a level that's very consistent with human social memory," said Jason Bruck, from the University of Chicago in a press release.
Researchers speculate that this social recognition can be more long-lasting than human's face recognition as human face features tend to change over time but a dolphin's signature whistle remains the same.
An earlier study found that dolphins use signature whistles that act like names. Researchers from Scotland's University of St. Andrews found that bottlenose dolphins create unique signature whistles to distinguish themselves from each other and to identify themselves by the sound of their own chirps. They are also capable of imitating other dolphins' signature whistles.
The study looked into data from 53 different bottlenose dolphins at six facilities. Bruck played a recording of a signature whistle of an old mate the dolphin lived with previously to see if it recognized the whistle. Recognition was measured by how they responded to familiar calls versus calls belonging to dolphins they had never met.
Bruck noticed that dolphins tend to get bored when constantly hearing whistles of other dolphins they never met. However, they displayed much enthusiasm when a recording of a whistle they were familiar with was played.
"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."
To test whether this enthusiasm was a sign of recognition, Bruck replayed the whistle of an unfamiliar dolphin of the same age and sex as the familiar animal. How frequently and to what degree these dolphins responded to the recorded whistles was recorded.
Researchers found that dolphins responded significantly more to whistles from animals they once knew, even if they had not heard the calls in decades. This led the team to conclude that dolphins retain lifelong memories of each others' whistles.
Bottlenose dolphins have an average life expectancy of about 20 years but can live up to 45 years or more in some cases. According to Bruck, dolphins have the longest pure memory than any other non-human species. While an elephant can remember its mother after 20 years, researchers are yet to determine whether the animal's memory capabilities extend beyond family ties.
Researchers are yet to determine the mechanism behind a dolphin's long social memory abilities. Some experts speculate that it could be becasue of the "fission-dustion" model dolphins live by. They sometimes break away from one group and "fuse" with another. This may have given rise to the need for good memory capacity. Other scientists are of the opinion that this powerful memory of dolphins could be just one facet of the advanced mind that evolved in dolphins for other reasons.
"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."
Further studies need to be conducted to analyze how similar dolphins' signature calls are to human words. Though studies have shown that these whistles are used as names, researchers have not been able to determine what these whistles signify in a dolphin's mind or whether the whistle stands for something in a dolphin's mind the way a person's name does for humans. Bruck plans to look into this theory in his further researches.
