Scientists discovered that each dolphin gives itself a name in the form of a sound-pattern which is unique to him and then publishes it among the pod (a pod usually is around 12 members). In this way, dolphins call each other distinctly. a dolphin who wants to call his friend, will whistle the name of the pod member and in response the pod member will whistle his name back to confirm that he is present and heard the call. Names are often used when dolphins are in large groups, such as when several pods meet in the ocean, they exchange whistles in order to introduce themselves and get to know each other. More names are used when one of the dolphins moves away from the pod. In this case, the other dolphins call the dolphin so it will not go too far or to look for a missing pod member. It also turns out that dolphins are able to recognize that they have been called even when the voice is produced by someone other than a dolphin!
This discovery was made by a group of scientists who were on a boat (off the east coast of Scotland) and recorded the sound while a dolphin announced his presence, the researchers then Responded with the same whistle as a response to the call.