Dolphins call each other by name, using individual signature whistles.
They respond to hearing the sound of their own whistle by calling back, a team of Scottish scientists has found.
But they ignore names that are not theirs – even if they belong to other members of their own social group.
Scientists already knew that every dolphin develops a signature whistle early in life.
Dolphins often broadcast their signature whistle, and exchange whistles when they meet at sea.
But the new study confirms that they use the whistles in the same way humans use names, as identity tags for addressing individuals.
Scientists made the discovery while studying a group of wild bottlenose dolphins off the Scottish east coast.
The team from the University of St Andrews used underwater speakers to play synthetic versions of dolphin signature whistle recordings.
They found that individual dolphins responded to hearing their own 'name' by calling back with the same signature whistle. But the same response was not seen at the signature whistles of other dolphins.
It made no difference if the wrong whistles belonged to dolphins within the group or strangers from outside.