The Hawaiian goose (Branta sandvicensis), or nene, is the state bird of Hawaii and is among the most isolated, sedentary and threatened of all waterfowl. It is the sixth most endangered waterfowl species worldwide. The native Hawaiian name, Nene, is derived from their distinctive "nay-nay" vocalization. It is a species endemic to the Hawaiian Islands - it formerly bred on all or most of the Hawaiian Islands, but currently is restricted to Hawaii, Kauai and Maui. It is a medium-sized goose spending most of its time on the ground, although some individuals fly daily between nesting and feeding areas. Unlike other waterfowl, they mate on land. Hawaiian geese have a black face and crown and cream-colored cheeks. The neck is pale grayish streaked with black and has a narrow dark ring at the base. The body plumage and folded wings are gray-brown with transverse barring. The bill, legs and feet are black and the iris is dark brown. Both sexes are similar in appearance, but males typically are larger. Unlike most other geese, Nene are non-migratory, generally only island wide movement is known to occur. Nene have also been called "semi terrestrial," in that the toe webbing is reduced. The reduction of webbing between their toes enables them to walk more easily on the rugged lava flows.