Emerging research
shows that dolphins have the ability to remember one another's signature call for at least 20 years. This talent may even surpass humans' proficiency to remember one another based on appearance alone.
Every dolphin possesses a distinctive whistle which is used as a signature call and remains unchanged throughout its life. This identification technique is more reliable than facial recognition because it is based on a fixed auditory signal. Facial features change over time, making accurate identification difficult.
This type of "social memory" surpasses the abilities of elephants, primates, and all other intelligent animals that have been studied in this way, said Jason Bruck, who worked on the study while earning a PhD at the University of Chicago.
"This research shows that dolphins have the potential for lifelong memory for each other regardless of relatedness, sex or duration of association. This is the first study to show that social recognition can last for at least 20 years in a nonhuman species," Dr. Bruck said.
"This shows us an animal operating cognitively at a level that's very consistent with human social memory. This is the kind of study you can only do with captive groups where you know how long the animals have been apart. To do a similar study in the wild could be almost impossible," he said.
Recorded signature whistles of 53 different bottlenose dolphins living at six different locations were collected for the study. The results were published in the journal Proceedings of the Royal Society of London B.
Dr. Bruck played a recording of signature whistles of a stranger that a dolphin had never heard before, which were not recognized by the dolphin. Then Dr. Bruck would introduce the call of a dolphin they had once known, and measure its reaction and behavior.
"When they hear a dolphin they know, they often quickly approach the speaker playing the recording. At times they will hover around, whistle at it, try to get it to whistle back," Dr. Bruck said.
For example, a female dolphin named Allie living at Brookfield Zoo (near Chicago) recognized and responded to a recorded signature whistle of a female dolphin named Bailey, now living at Dolphin Quest in Bermuda. The dolphins shared a pool 20 years and six months ago while living together at Dolphin Connection in Florida Keys.
Dolphins are estimated to live about 20 years in the wild and 45 years in captivity. It is possible that their ability for social memory could last an entire lifetime.
This study is the longest social memory analysis in animals. Anecdotal reports of elephants recognizing their mothers after 20 years of separation are the closest comparisons.
"We know they use these signatures like names, but we don't know if the name stands for something in their minds the way a person's name does for us. We don't know yet if the name makes a dolphin picture another dolphin in its head," Dr. Bruck said.
