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Masked Booby | Sula dactylatra
Maskergent | Bobo enmascarado
The Masked Booby is the largest booby of the tropics. It breeds on bare, remote islets and forages far out at open sea, so it is rarely seen from the coast. In the guide area its colonies are on the Campeche Bank in the Gulf of Mexico and on islands off the Pacific coast of Mexico; further south it is a scarce visitor at sea.
Voice
Silent at sea, noisy at the colony. The male gives a falling, whistled fiew, the female a loud, hoarse honking honk.
Recording: Eric S. J. Tan — CC BY-NC-SA 4.0 · converted to mono · xeno-canto
Identification
75–85 cm, bulky, with a wingspan of over one and a half metres. Adults are white, with black primaries and secondaries giving the wing a broad black trailing edge, and a black tail. The bare skin around the bill and eye forms a black mask; the bill is yellow to greenish yellow, the eye yellow and the legs olive-grey. The sexes are alike but differ in voice. Juveniles are brown on the head, neck and upperparts, with a white collar on the hindneck and a white belly; the bill is greyish. Adult plumage is reached in about three years.
Confusion species
Nazca Booby Sula granti, on the Pacific side, is almost identical but has an orange-pink bill; juveniles of the two species often cannot be safely separated in the field. The white morph of Red-footed Booby Sula sula is smaller, with a white tail, red legs, a blue bill and a black carpal patch on the underwing. Juvenile Masked Boobies resemble Brown Booby Sula leucogaster and Cocos Booby Sula brewsteri, but are larger and have a white collar separating the brown hood from the mantle.
Habitat
Open, deep water far offshore, where the birds plunge steeply from a great height for flying fish and other schooling fish. They breed on bare ground on level parts of rocky islets, sand cays and volcanic islands, without a real nest. Of the two eggs almost always only one chick is raised: the older chick ousts the younger.
Where the bird is most at home, classified by the vegetation units of Mexico and Central America.
Range and movements
On the Gulf side the species breeds on the Campeche Bank, including Arrecife Alacranes, Cayo Arcas and the Triángulos; away from the colonies it is scarce at sea in the Gulf of Mexico and the Caribbean Sea to Panama. On the Pacific side it breeds on the Revillagigedo Islands and on a few islands off the coast of Mexico, and is a scarce visitor at sea to Costa Rica and Panama. Birds of the Gulf of Mexico and the Caribbean belong to the nominate form S. d. dactylatra; those of the Pacific islands off Mexico are usually placed in S. d. californica. Outside the guide area in all tropical oceans.
- Resident
- Summer visitor (c. Apr–Sep)
- Winter visitor (c. Oct–Mar)
- Passage (Mar–Apr, Oct–Nov)
- dark = core range, pale = thinly spread
How and when to look
Chances are best on pelagic trips and on boat trips to remote islands and reefs, such as the Revillagigedo Islands or Arrecife Alacranes. For a large, white booby with a black trailing edge to the wing, bill colour is the key feature to separate it from Nazca Booby.
Conservation status
Not threatened. In the guide area the population is spread over few colonies. Threats are introduced rats, cats and other predators, disturbance, the taking of eggs and chicks and entanglement in fishing gear.
Scientific name
Sula dactylatra | Lesson, 1831
Lesson described the species in 1831 and placed it straight away in the genus where it still stands. The genus Sula was introduced in 1760 by Brisson. Sula goes back to súla, the Old Norse and Icelandic word for the gannet; the name passed to the boobies. dactylatra combines Greek daktulos 'finger' and Latin ater 'black': 'black fingers', after the splayed black wingtips in flight. The specimen the first description was based on came from Ascension Island (South Atlantic).