Two dolphins have been recorded having a conversation for the first time after scientists developed an underwater microphone which could distinguish the animals' different "voices".

Researchers have known for decades that the mammals had an advanced form of communication, using distinctive clicks and whistles to show they are excited, happy, stressed or separated from the group.

But scientists have now shown that dolphins alter the volume and frequency of pulsed clicks to form individual "words" which they string together into sentences in much the same way that humans speak.

Researchers at the Karadag Nature Reserve, in Feodosia, Ukraine, recorded two Black Sea bottlenose dolphins, called Yasha and Yana, talking to each other in a pool. They found that each dolphin would listen to a sentence of pulses without interruption, before replying.