Dolphins Have Lifelong Social Memories, Longest in Non-Human species [VIDEO]

An interesting find about dolphins reveals that these marine mammals can remember the signature whistle of another dolphin for at least 20 years, making it the longest social memory ever recorded among non human species.

A growing number of studies in the past have revealed that dolphins are intelligent and have skills in common with humans.

Adding to this body of evidence, a new study conducted by researcher Jason Bruck, PhD graduate from the University of Chicago, revealed that dolphins can recognize the signature whistle of their old tank mates even after being separated for more than 20 years. This finding provides a clear indication that these intelligent marine mammals have a level of cognitive sophistication that is equal to a few species such as chimps, elephants as well as humans.

Studies in the past have revealed that bottlenose dolphins use signature whistles to identify themselves in a social group. Their talent for social recognition is long lasting when compared to the facial recognition among humans because human features undergo changes over a period of time but the dolphin's signature whistle remains the same over several decades. This is a key feature that helps them to maintain a long lasting social memory.

In order to work out how the dolphins remember their old tank mates, Bruck worked on data collected from 53 dolphins from six sites that had been moved for breeding purposes, which included Brookfield Zoo near Chicago and Dolphin Quest in Bermuda.

He conducted his study on captive groups as there the duration of separation can easily be determined, but a similar study in the wild is challenging and impossible.

In his experiment, Bruck played the recordings of the signature whistle of old tank mates.

He first played a series of recording of signature whistles that the target dolphin had never heard before. The signature whistle was new and unfamiliar. Prior to this study, Bruck found that on listening to an unfamiliar signature whistle, dolphins get bored quickly. Later he played a recording of a signature whistle that belonged to an animal that had once lived with the target dolphin.

On listening to the familiar signature whistle, the dolphin immediately responded to that tune.

"When they hear a dolphin they know, they often quickly approach the speaker playing the recording," Bruck said in a press statement. "At times they will hover around, whistle at it, try to get it to whistle back."

Bruck added, "If they are unfamiliar with the call they are more likely to ignore what I am playing. It's unprecedented in the study of animal behaviour to find memories this long."

For this study, Bruck experimented on Allie and Bailey. Allie is a female dolphin currently at  Brookfield Zoo while Bailey is a female dolphin in Bermuda. When Allie was 2 and Bailey 4, they had shared a tank together at Dolphin Connection in the Florida Keys. And  20 years and six months after they were separated, Bailey recognized the signature whistle of Allie.

This kind of performance even after being separated for decades is typical. Thus, Bruck concluded that dolphins maintain lifelong memories of their old mates' 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."

Next Bruck plans on testing whether signature whistles evoke a representational mental image of the dolphin.

The study is documented in the Proceedings of The Royal Society.