Dolphins

Oceanic dolphins are a widely distributed family of dolphins that live in the sea. Close to forty extant species are recognized. They include several big species whose common names contain \"whale\" rather than \"dolphin\", such as the orca and pilot whale. Dolphins have streamlined bodies and two limbs that are modified into flippers. Though not quite as flexible as seals, some dolphins can travel at speeds 29 km/h (18 mph) for short distances. They travel in large pods, which may number a thousand individuals in some species. Each pod forages over a range of tens to hundreds of square kilometers. Dolphins communicate by sound, producing low-frequency whistles, and also produce high-frequency broadband clicks of 80-220 kHz, which are primarily used for echolocation. After the gestation of 10 to 18 months, females give birth to a single calf. Some species are well adapted for diving to great depths. They have a layer of fat, or blubber, under the skin to keep warm in the cold water. Dolphins are well known for their intelligence and occasionally feature in literature and film. They are sometimes kept in captivity and trained to perform in shows.