Dolphins Remember Companions Even After Two Decades of Separation

For long, elephants were believed to have a good memory, but new research has shown that dolphins are better than elephants at remembering their companions.

Dolphins can remember their companions' calls even after 20 years, which is the longest ever social memory recorded for a non-human species, according to a study by Jason Bruck from the University of Chicago.

Previous research has shown that dolphins assign unique "names" based on whistle patterns and are more likely to respond to calls of those they have known earlier than calls of an unfamiliar dolphin.

The new research found that dolphins can not only identify but even remember the whistles of their former tank companions even after a gap of two decades.

"This shows us an animal operating cognitively at a level that's very consistent with human social memory," said Jason Bruck, from University of Chicago's program in Comparative Human Development and study author.

The study included data from 53 bottlenose dolphins from six different facilities that had taken care of the dolphins in rotation. All the facilities had kept records of the dolphins that stayed together.

The dolphins in the study were first made to listen to whistles of stranger dolphins. Researchers found that "dolphins get bored quickly listening to signature whistles from dolphins they don't know."

Once these dolphins became accustomed to hearing unfamiliar sounds, researchers started playing records of former dolphin companions.

It was observed that the dolphins' curiosity increased when they heard calls of a former tank-mate.

"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."

Researchers conducted another test to see if they remembered their companions; Bruck played a recording of an unfamiliar dolphin that resembled the companion in terms of age and gender.

All tests showed the same result- dolphins consistently responded to the whistles of known companions.

Dolphin Reunion after 20 Years

Allie, a dolphin, currently lives at the Brookfield Zoo while Bailey lives in Bermuda. The two female dolphins were last kept together at Dolphin Connection in the Florida Keys. At that time Allie was about 2 years old while Bailey was 4.

Researchers found that the dolphins instantly recognized the whistles even after 20 years of separation.

In comparison, the elephant is the only other non-human species that can remember its mother after 20 years. Researchers attribute dolphins' strong memory to the kind of social structure they live in. Dolphins typically stay as a group, but later on they break from a group and join another group, following the "fission-fusion model". Living in such a social structure would require good memory. Also, researchers believe, that memory in dolphins could also represent their advanced cognitive skills.

Dolphins are fascinating animals; they can not only solve complex math problems but are also self-aware with complex personalities. Dolphins are known to take special interest in knowing pregnant women and will help people from sharks. However, they are also known to kill for fun and even assault divers. Many researchers believe that dolphins are non-human people.

"Why do they need this kind of memory? I'm not sure they do," Bruck said in a press release. "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."

The study is published in the current issue of the Proceedings of the Royal Society of London B.