Bruck used that to test dolphins' memories. He studied dolphins from six breeding facilities that rotate the animals among themselves -- and, in the process, keep detailed records of which dolphins shared tanks, and when. There were more than 50 animals in all. Bruck first recorded each dolphin's unique whistle. And then he played it back to the dolphins' former tankmates using underwater speakers. (As controls, Bruck both habituated the dolphins to unfamiliar whistles -- thus eliminating the possibility that the animals were simply responding to the novelty of speaker-based sound signatures -- and alternated those whistles with the calls of unfamiliar dolphins.) The point? To test whether the dolphins would recognize each others' whistles, even after years-long stretches of separation.

The findings? The dolphins did, indeed, seem to remember each other. The whistles of the dolphins' former tankmates resulted in the dolphins doing things like purposely bumping into a speaker, or (even more sadly) whistling at it -- "trying," Nature notes, "to make it whistle back."

And that recognition behavior held, even more interestingly, no matter how long a pair had been separated. A dolphin named Bailey had been living apart from a former tankmate, Allie, for more than 20 years. Yet Bailey, in Bruck's experiment, seemed to recognize Allie's "name" -- her signature whistle -- despite the temporal distance. Bailey's recognition of Allie, Nature puts it, represents "the most durable social memory ever recorded for a non-human."

Bruck just published the results of his research in the Proceedings of the Royal Society B. And while it's unclear what his findings might mean about dolphins' memories overall -- he was testing name recognition, not circumstantial or emotional memories -- there's some reason to think that dolphins' memories stretch beyond rote recognition itself. In tests that broadcast the signature whistles of "extremely dominant males," for example, Bruck found that females responded with "exceptional interest." "There was also a lot of posturing from the males," Bruck noted. And "some young ones would just go ballistic."

In other words, dolphins may well have the capacity for relatively complex memories -- memories that associate individuals with actions. Memories that can last for decades. So, should you find yourself doing dealings with a dolphin, try your best to stay on its good side. Twenty years is a long time.

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