Not only do dolphins mourn their dead, call each other by distinct names, protect their faces with sponges and recognize themselves in mirrors, but now a new study reveals that dolphins have phenomenal memories. Even after being separated for 20 years, dolphins remember their tank mates’ whistles.
Research published in February found that dolphins have unique signature whistles which they use to address those they are close to. Scientists had previously observed that dolphins emit unique whistles to identify themselves to other dolphins. Jason Bruck made the latest discovery about dolphins, that they have long-term social memories, while doing research for his Ph.D. in the University of Chicago’s program in Comparative Human Development.
Bruck drew on data kept on 53 different bottlenose dolphins at six facilities that are part of a breeding consortium through which dolphins are rotated. The facilities have kept records that go back decades about which dolphins had lived together.
To get a sense of how dolphins responded to whistles that were familiar to them versus those made by dolphins whom they did not know, Bruck played recordings of whistles from unfamiliar dolphins to the animals he was studying. Dolphins, he notes, “get bored quickly listening to signature whistles from dolphins they don’t know.” But when Bruck played a whistle from a dolphin who had been a former tankmate, the dolphin being tested would swim quickly over to the speaker and “hover around, whistle at it, try to get it to whistle back.”
One particularly notable example involved Allie, who currently lives at the Brookfield Zoo in Chicago, and Bailey, a female who now lives in Dolphin Quest in Bermuda. Allie was two and Bailey was four when they had last been together, at Dolphin Connection in the Florida Keys. While twenty years and six months had passed since they had been together, Bailey recognized Allie’s whistle.
Bruck’s study shows that dolphins have memories that are the longest in a non-human species (elephants have been found to remember their mothers after 20 years). He speculates that dolphins may have evolved the ability to have such long memories because of the social connections they form; in the open ocean, dolphins break apart from one group and “fuse” or join with other groups many times over. Or, their memory could be just yet another “facet of the advanced mind that evolved in dolphins for other reasons.”
As Bruck acknowledges, his research was carried out on captive dolphins; he says that it would be “almost impossible” to conduct a similar study in the wild as it was necessary to know how long the dolphins had been apart from each other. Bruck’s findings offer yet another reason to take into account how dolphins in captivity are affected emotionally and otherwise by an experience none of us would want to be in. A dolphin rushing to a speaker when he or she heard a familiar whistle — the sign of a friend last heard two decades ago — suggests how much it might mean for long-separated dolphins like Allie and Bailey to be reunited.
Bruck’s study also offers further evidence, as one Emory University professor has argued, that dolphins — and, whales, elephants and chimps (who also hold on to their memories just as we do) — deserve human rights because of their highly developed cognitive, emotional, social and other abilities.
Can you remember the sound of someone’s voice from 20 years ago?
Photo from Thinkstock
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