petrel (pĕˈtrəl) [key], common name given various oceanic birds belonging, like the albatross and the shearwater, to the order known commonly as tube-nosed swimmers. There are two families of petrels: the storm petrels (Hydrobatidae) and the diving petrels (Pelecanoididae). Many skim the waves so closely that they give the appearance of walking on the water. They are tireless fliers by day and at night rest on the water; many return to land only to breed. Two species that frequent the Atlantic coast off North America are Wilson's petrel, Oceanites oceanicus (also called Mother Carey's chicken), a surface skimmer and habitual boat follower, and Leach's petrel, Oceanodroma leucorhoa, which has a bounding, erratic flight and breeds on islands off the New England coast. The giant petrel, or giant fulmar (the size of an albatross), and the auklike diving petrel, Pelecanoides urinatrix, are both found in the Southern Hemisphere; the fulmar ( Fulmarus glacialis ), or fulmar petrel, inhabits the North Atlantic. The giant petrel is actually a member of the family Procellariidae (shearwater family). Petrels are classified in the phylum Chordata, subphylum Vertebrata, class Aves, order Procellariiformes, families Hydrobatidae and Pelecanoididae.