Could you recognize the voice of a friend you hadn’t heard for a year? How about 20 years? A dolphin named Bailey recognized her friend Allie’s voice after not seeing or hearing her for two decades!
Bailey and Allie are bottlenose dolphins (Tursiops truncates) that once lived together in a Florida breeding facility. When scientists played a recording of Allie’s “signature whistle” for Bailey recently, she responded by whistling back at the underwater speaker and nudging it, as if she was looking for her old pal.
As early as four months, every bottlenose dolphin creates a whistle that becomes its signature to other dolphins. To test if dolphins would remember old friends’ whistles, scientists installed an underwater speaker in a tank and played the sounds of several dolphins that were unfamiliar to the test dolphin. The dolphin did not respond.
Then they played the signature whistle of a dolphin that the test subject had once known but had not seen in a long while. The subject was more likely to nudge the speaker or whistle back at the speaker when it heard an old friend’s whistle, as if trying to elicit a response. Dolphins, it seems, have excellent memories. This experiment was performed with several dolphins and always produced the same results.
Scientists don’t know how these marine mammals retain the memory of others’ whistles. It could be that they simply add each unique whistle to their own vocal repertoires. But scientists suspect that dolphins actually remember the other dolphin that originally created the whistle. As proof, dolphins respond more strongly to whistles of the opposite sex.
The ability to remember is very valuable in the wild. For instance, by remembering individual whistles, dolphins can remember which others were friendly or not, then choose to join or avoid them.
This recognition and awareness suggests that dolphins have a consciousness seen only in some primates (such as humans and chimpanzees), and also in elephants — who are also known for their excellent memories.