43 - 48 cm. 125 cm wingspan. 567 - 935 g. Large size. Upperparts gray-brown, sides of head dark. Throat white, underparts whitish. Can show a whitish band on the base of tail. Wings long, thin, with the inferior margin dark. Bill yellowish, dark on tip and hook-shaped, near the nasal holes, have a little pipe that help to remove excess salts. Legs webbed (fingers united by a membrane), flesh color. The male is usually more robust but males and females are very similar. The chicks are dark brown, similar to the rocks where the nests are placed, when grow, the dark down turns gray.