Turtles often travel long distances to lay their eggs on the beaches where they were born. Many species have suffered through destruction of their breeding sites as well as being hunted for food and their shells. Unlike tortoises, turtles cannot retract their heads into their shells. Marine turtles are generally herbivores, feeding mainly on sea grasses.
Freshwater turtles eat a range of animals including worms, frogs, and fish.
They are excellent swimmers, having legs that are modified to oarlike flippers but which make them awkward on land. The shell is more streamlined and lighter than that of the tortoise. Other turtles suffer because their eggs are taken by collectors and their breeding sites are regularly destroyed, often for tourist developments. The world's rarest turtle is the Kemp's ridley , which breeds only at a single site in the Gulf of Mexico. A new species of turtle was discovered in Mexico in 1997.