Killer whales have the closest-knit family groups. There are about 17 or 18 in a group of killer whales. There are a dozen who live in a bottle-nosed dolphin group. Family units form schools of 100-1,000 dolphins. Schools consists of a dominant male, several females and their yound and few immature dolphins of both sexes. They communicate by other means of sounds called phonations. They make phonations by making air-filled sacs connected to their blowholes. These phonations resemble the clicking and whistlings sounds of echolocation.
Dolphins swim by moving their flukes up and down. They use their flippers for sudden stops and making sharp turns. They can dive more than 1,000 feet (300 meters).
