As mammals, baby dolphins survive on milk for the first few years of life, although they may learn to catch fish at only a few months of age. Over time, dolphins depend less on milk and more on fish and squid.
As cetaceans, dolphins are closely related to whales and porpoises. The killer whale is the largest species of dolphin, growing up to 30 feet in length and weighing as much as 10 tons. Considered to be highly intelligent animals, dolphins live in pods of up to 12 members and have a sophisticated system of clicks for communication. Dolphins have displayed acts of interspecies altruism, such as in cases of rescuing stranded swimmers and even other cetaceans.