To make the discovery, a team from St Andrews University followed a pod of dolphins off the coast of Scotland.
They used underwater microphones to record the exchanges of whistles.
Previous research showed captive dolphins had unique whistles but, until the study, it had never been heard in the wild.
Biologist Dr Vincent Janik, said: ‘Our results show dolphins provide identity information through signature whistles when they encounter others at sea.
‘Given the similarities between humans and dolphins in the acquisition of sound, it is of great interest to see how signals are used in wild dolphins.’
The news comes after conservationists called for a Declaration of Rights for Cetaceans, claiming dolphins should be treated as non-human ‘persons’.