Present in all of the world's oceans, the dolphin is a migratory animal. They are very sociable and live in groups composed of males, females, and children who maintain strong relationships with each other. They communicate through ultrasound - a sound which is too high-frequency to be heard by the human ear. According to a study by Stephanie King and her colleagues at St. Andrews University, these incredible marine mammals are each able to emit their own unique sound to communicate with each other. You could compare this ingenious system to the way we humans use names to identify ourselves. Despite this, when dolphins reach puberty they tend to split from the group. Female dolphins tend to stay with their mothers, whilst males will split off in pairs. Occasionally some dolphins will choose to spend their lives outside of these groups. This phenomenon of solitary dolphins remains a mystery to scientists. Studies so far suggest that this isolation is either voluntary, accidental, or pathological.