Masked Booby

The largest species of booby, the masked booby ranges from 75 to 85 cm (30 to 33 in) long, with a 160–170 cm (63–67 in) wingspan and 1.2–2.2 kg (2.6–4.9 lb) weight. It has a typical sulid body shape, with a long pointed bill, long neck, aerodynamic body, long slender wings and pointed tail. The adult is bright white with dark wings and a dark tail. The sexes have similar plumage with no seasonal variation, but females are on average slightly heavier and larger than males. The bare skin around the face, throat and lores is described either as black or blue-black. It contrasts with the white plumage and gives a mask-like appearance. The bill of the nominate subspecies is pale yellow with a greenish tinge, sometimes greyish at the base. Conical in shape, the bill is longer than the head and tapers to a slightly downcurved tip. Backward-pointing serrations line the mandibles. The primaries, secondaries, humerals and rectrices are brown-black. The inner webs of the secondaries are white at the base. The underwing is white except for the brown-black flight-feathers that are not covered by the white coverts. The legs are yellow-orange or olive. The iris is yellow. The subspecies differ slightly in size and sometimes also in the colour of the irises, bill, legs and feet. The race melanops has an orange-yellow bill and olive-grey legs, the race tasmani has dark brown irises and dark grey-green legs and the race personata has olive to blueish-grey legs. For the subspecies tasmani and the nominate dactylatra, during the breeding season, the leg colour of male birds contains more yellow-red than those of the females. The juvenile is a streaked or mottled grey-brown on the head and upperparts, with a whitish neck collar. The wings are dark brown and underparts are white. Its bill is yellowish, face is blue-grey and iris a dark brown. Older immature birds have a broader white collar and rump, and more and more white feathers on the head until the head is wholly white by 14 to 15 months of age. Full adult plumage is acquired three to four months before the bird turns three years old. The masked booby is usually silent at sea, but is noisy at the nesting colonies. The main call of male birds is a descending whistle; that of females is a loud honk. The adult masked booby is distinguished from the related Nazca booby by its yellow rather than orange bill, larger size and less distinctive sexual dimorphism. The latter nests on steep cliffs rather than flat ground. The white morph of the red-footed booby is similar but smaller. Abbott's booby (Papasula abbotti) has a more wholly black upperwing, and a longer neck and tail and larger head, while the Cape gannet (Morus capensis) and the Australasian gannet (Morus serrator) have a buff-yellow crown, shorter tail, white humerals and a grey rather than yellowish bill. The juvenile masked booby resembles the brown booby (Sula leucogaster), though adults of that species have clearly demarcated brown and white plumage.