Absolutely amazing memory of dolphins is what the below article says , I loved reading it and thought of sharing with you

Researchers from the University of Chicago, in the first week of August 2013, revealed that dolphins had the longest memories among the non-human species. Researchers declared that even if these dolphins were separated for more than 20 years, they were capable of recalling the whistles of their former companions.

The researchers believed that the long-term memories of dolphins were a product of complex social connections from which they have evolved.

During the study, the researchers used the information on relationships between 56 captive bottlenose dolphins. These dolphins moved for the purpose of breeding between six diverse aquariums and zoos in Bermuda as well as the US. The records which dated back to decades were used to find out which dolphins were housed together.

Thereafter, the researchers played the recordings to these dolphins on the underwater speakers. The recordings were the signature whistles of dolphins, with which they had once lived. Their responses were then measured.

The lead researcher of the study explained that these dolphins approached the speakers for longer duration in case they recognised the call. They maintained contact with the speaker for a longer time. On the other hand, when they were unfamiliar with the call, they ignored these recordings from the speaker. It is unique to find such behaviour in non-human species. He further  explained that the response of this kind was very typical. In comparison to the unfamiliar calls, there was absolutely clear pattern in data where dolphins reacted primarily more to whistles of those dolphins with whom they had once lived and had not seen or heard since decades.

The researchers, in the meanwhile, believed that the complex nature of social systems of dolphin was responsible for long term memory effect. In the ocean, the dolphins have fluid social arrangement which is scientifically called fission-fusion model. According to this model, the dolphins can exit one group and enter others, several times during their lifetime.

Therefore, it becomes important for them to recall calls of those dolphins with which they had previous encounters. This was important so that they could decide whether they should approach or not the dolphin of which they heard the whistle.

The researchers explained that the ability of the dolphins to recall events hinted towards the fact that the cetaceans have a level of cognitive complexity in comparison to the humans, elephants and chimpanzees.

Elephants also have the capability of long memory of up to 20 years. But, there is very limited evidence of their abilities beyond the family relations.