White-sided dolphins swim in herds of thousands. Members form a close-knit group and will often care for a sick or injured dolphin. Animals that live in such big social groups develop ways to keep in touch. Each dolphin identifies itself by a unique -whistle. Staying close helps, too. Young dolphins communicate with a touch of a flipper as they swim beside adults. Pacific dolphins swim in forms with other dolphins and sea lions, leaping from the water in spirited somersaults. Dolphins also use this hitchhiking trick with their own cousins: sometimes they ride on the waves of large whales. Common dolphins travel in pods of up to 2,000 animals. This is the classic dolphin of Greek and Roman mythology.