Dolphins have longest memories in animal kingdom

There's a saying that elephants never forget, but a new study conducted by the University of Chicago indicates that it is dolphins that can remember call of another dolphin decades later, according to a paper in Wednesday's Proceedings of the Royal Society B.

After examining more than 50 bottlenose dolphins, Jason Bruck, a University of Chicago postdoctoral scholar, found that dolphins could remember the signature whistles of former tank mates for more than 20 years, which is the longest among non-human species.

Bailey the dolphin hadn't seen another dolphin named Allie since the two juveniles lived together at the Dolphin Connection in the Florida Keys. Allie ended up in a Chicago area zoo, while Bailey got moved to Bermuda.

Yet over 20 years later, Bailey recognized and reacted to Allie's distinctive signal when researcher played it on a speaker.

Other dolphins had similar steel-trap memories. And it's not just for relatives.

"It's mind-blowing; I know I can't do it," Bruck said. "Dolphins in fact have the longest social memory in all of the animal kingdom because their signature whistle doesn't change."

Studies have shown that monkeys can remember things for about four years and anecdotes have elephants remembering for about 10, Bruck said.

For Bruck, 33, it's as if a long-lost classmate from middle school called him up and he would be able to figure out who it was just from the voice.

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."

Outside dolphin researchers have praised the work, saying the next effort is to see whether somehow the dolphins visualize their old buddies when they hear the whistle.

Bruck said he is working on that. "That's my goal -- show whether the call evokes a representational mental image of that individual."