Every Dolphin have individual name & they call each other by name! One study found that Dolphins stay together in a group & need a system to stay in touch with each other. So, each Dolphin develop a unique whistle of it (like names in case of human beings) i.e. its signature whistle. Then other Dolphins can copy that whistle to call that particular Dolphin (like we call other human beings by their name). On hearing its unique whistle made by other Dolphins, such Dolphin responds to them! So, Dolphin responds when called by its name by way of a special whistle just as we respond when called by our name!