Often after people lose someone dear to them they try to jog their memories of the deceased by looking at old photos, reading something the person wrote and, mainly, by mentioning his or her name in certain situations. It seems that people are not the only ones who do this: According to a study conducted by Israeli scientists at the Eilat campus of Ben-Gurion University of the Negev, dolphins engage in similar behavior.
Researchers led by Tan Morgan – a doctoral student from Scotland who is studying marine biology at BGU – found that dolphins in the Red Sea reef emit unique sounds, or vocal signatures, that were used by dolphins that lived among them at one time, including some that had even died.
Scientists embarked on the study about three years ago, when Morgan began to record sounds made by five dolphins in various parts of Eilat's Dolphin Reef. The original purpose of the study – conducted under the auspices of Prof. Nadav Shashar, a marine biologist, and Dr. Arik Kershenbaum, a zoologist from the University of Cambridge – was to examine whether there is a connection between the sounds created by the dolphins and the environment in which they live.
The recordings were analyzed and classified by means of a spectrogram, a visual form of audio-frequency analysis. Morgan found that in several recordings, signature whistles were documented that did not match those of the dolphins being studied. The signature whistle, he explained, is a distinctive sound that every dolphin develops during its early years. In the same way that human beings use names, it is a means for the dolphin to be identified by other members of the pod.
“It’s not a voice – it’s a unique whistle, it’s more like their name,” Morgan told Haaretz, adding that, “During the first year of their lives they (the dolphins) learn how to make a lot of different sounds, they imitate some of the other dolphins, some invent their own, and finally they create a whistle that is unique to them, which no other dolphin uses. The moment it develops the whistle, that’s its name, its signature whistle.”
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What is unique among dolphins is that each one consistently emits its own whistle, and only very rarely produces that of another dolphin. When Morgan analyzed the recordings, however, she was surprised to discover the signature whistles of three dolphins that no longer live in the reef. One of them, a dolphin named Dicky, was returned to the Black Sea in 1998; the other two, Dana and Shai, died in 2013 and 2015, respectively.
“At first, she didn’t believe it and we thought that maybe it was a mistake,” said Shashar. “An in-depth examination of the audio files revealed that Morgan was not mistaken, and that the dolphins being studied (it’s not yet known exactly which of them) repeated the signature whistle of their friends, who are no longer with them."
Shashar added that the importance of the research is that for the first time it presents empirical proof that an animal is capable of remembering other members of its species even when they are no longer alive – in effect, to express a profound memory.
“When we talk about memory and a collective perception, we (human beings) feel that some of the things that make us unique are that we remember the past and the generations that preceded us,” he said. "In this case we see that there are other animals that are capable of relating to someone that they know is dead. That means that in cognitive terms they have an individual memory that is also preserved over time.”