Dolphins are capable of “highly developed spoken language” which closely resembles human communication, scientists have suggested.

While it has long been acknowledged dolphins are of high intelligence and can communicate within a larger pack, their ability to converse with each other individually has been less understood.

But researchers at the Karadag Nature Reserve, Feodosia, Crimea, believe the pulses, clicks and whistles – of up to five “words” – made by dolphins are listened to fully by another before a response is made.

“Essentially, this exchange resembles a conversation between two people,” wrote lead researcher Dr Vyacheslav Ryabov in the study, published in the journal Mathematics and Physics.

Dr Ryabov said each pulse produced by a dolphin “is different from another” in its time span and the frequencies it emits.

“In this regard, we can assume that each pulse represents a phoneme or a word of the dolphin’s spoken language,” Dr Ryabov wrote.

However: “The dolphin’s speech unfortunately lies beyond the time and frequency characteristics of the human hearing, and is thus unavailable to humans.”

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The study was conducted on two adult Black Sea bottlenose captive dolphins, a male named Yasha and a female called Yana.

The pair have lived for 20 years in a swimming pool, which measure just 27 metres by 9.5 metres and is four metres in depth. Without food rewards, a special audio system recorded the exchanges between the dolphins.

The noises emitted were of a different pattern to those produced in a pod.

Dr Ryabov continued: “The analysis of numerous pulses registered in our experiments showed that the dolphins took turns in producing pulse packs and did not interrupt each other, which gives reason to believe that each of the dolphins listened to the other’s pulses before producing its own.

“This language exhibits all the design features present in the human spoken language, this indicates a high level of intelligence and consciousness in dolphins, and their language can be ostensibly considered a highly developed spoken language, akin to the human language.”

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It has long been accepted that dolphins exhibit behaviours not found in other animals. For instance, they are known to have a self-identifying whistle and to communicate phrases to other dolphins in a pod.