booby, common name for some members of the family Sulidae, large, streamlined sea birds. Tropical and subtropical members of the family are called boobies; those of northern waters are called gannets. These birds have heavy bodies; long, pointed wings; long, wedge-shaped tails; and short, stout legs. They fish by diving on their prey from great heights and pursuing it underwater; air sacs under their skin cushion the impact with the water and provide buoyancy, as with pelicans. The masked, red-footed ( Sula sula ), and brown ( S. leucogaster ) boobies are found the world over; the Peruvian and blue-footed ( S. nebouxii ) boobies, on the west coasts of the Americas; and the Abbott's booby, in the Indian Ocean. The common gannet of the North Atlantic, Morus bassanus, breeds in the British Isles, in the Gaspé region of Canada, and on Bird Island in the Gulf of St. Lawrence. A Pacific gannet is one of the chief guano producers of the offshore islands of Peru. Gannets build crude nests of debris on narrow cliff ledges. The female lays a single egg, which she and the male incubate by covering it with their feet. Gannets have strong migration tendencies, while the boobies do not. The name booby is descriptive not only of the rather stupid facial expression of these birds, but also of their unwary, gullible behavior when hunted by man—a factor that accounts for their diminishing numbers. Boobies and gannets are classified in the phylum Chordata, subphylum Vertebrata, class Aves, order Pelecaniformes, family Sulidae.