Dolphins are considered to be one of the most intelligent aquatic species and now a new study published in the Proceedings of the Royal Society B reports that they have the greatest memory-storage capacity after humans.
The research, carried out by a scientific team from the University of Chicago, found that dolphins were able to recognize the whistle of a former member of their school, even if it went its separate ways 20 years before.
According to the study, these long-term memories are a product of complex social connections that dolphins developed over their eons of evolution.
The scientists based their research on relations among 56 bottlenose dolphins in captivity, brought together from six different aquariums in the US and the Bermudas for breeding purposes.
They first recorded their whistles and, decades later, played the recordings back to them on underwater loudspeakers to observe the dolphins' reactions when they heard the call of animals they had not seen for many years.
"When the dolphins heard a call, they were much more likely to hang around the loudspeakers for a long time," research chief Jason Bruck said.
According to Bruck, finding that dolphins recall such old memories is an "unprecedented" phenomenon in the study of animal behaviour.
The most astonishing case for researchers involved two female dolphins, Bailey and Allie, that had lived together during the first years of their lives.
Bailey instantly recognized Allie's whistle 20 years and six months after they had last been in contact.
The scientists concluded that dolphins also have a great ability to recall certain events, which places their knowledge-storing ability at a level comparable to that of humans, chimpanzees and elephants.