The masked booby (Sula dactylatra), also called the masked gannet or the blue-faced booby, is a large seabird of the booby and gannet family, Sulidae. First described by the French naturalist René-Primevère Lesson in 1831, the masked booby is one of six species of booby in the genus Sula. It has a typical sulid body shape, with a long pointed yellowish bill, long neck, aerodynamic body, long slender wings and pointed tail. The adult is bright white with black wings, a black tail and a dark face mask; at long, it is the largest species of booby. The sexes have similar plumage. This species ranges across tropical oceans, except in the eastern Atlantic and eastern Pacific. In the latter, it is replaced by the Nazca booby (Sula granti), which was formerly regarded as a subspecies of masked booby.
Nesting takes place in colonies, generally on islands and atolls far from the mainland and close to deep water required for foraging. Territorial when breeding, the masked booby performs agonistic displays to defend its nest. Potential and mated pairs engage in courtship and greeting displays. The female lays two chalky white eggs in a shallow depression on flat ground away from vegetation. The chicks are born featherless, but are soon covered in white down. The second chick born generally does not survive and is killed by its elder sibling. These birds are spectacular plunge divers, plunging into the ocean at high speed in search of prey—mainly flying fish. The species faces few threats; although its population is declining, it is considered to be a least-concern species by the International Union for Conservation of Nature (IUCN).
Taxonomy
The French naturalist René Lesson was a member of the crew on the La Coquille captained by Louis Isidore Duperrey on its voyage around the world undertaken between August 1822 and March 1825. In the multi-volume publication by Duperrey about the voyage, Lesson authored the ornithological sections. In his 1829 account of the visit to Ascension Island in the South Atlantic Ocean, Lesson mentioned encountering masked boobies, and in a footnote proposed the binomial name Sula dactylatra. Lesson subsequently provided a formal description of the masked booby in 1831. The specific epithet combines the Ancient Greek dactyl, meaning "finger", and the Latin ater, meaning "black". "Black fingers" refers to the splayed wingtips in flight. The Swedish zoologist Carl Jakob Sundevall described the species as Dysporus cyanops in 1837 from a subadult collected in the Atlantic Ocean on 6September 1827. The species name was derived from the Ancient Greek words cyanos, meaning "blue", and ops, meaning "face".
The English ornithologist and bird artist John Gould described Sula personata in 1846 from Australia, the species name being the Latin adjective personata, meaning "masked". Gould adopted the name Sula cyanops in his 1865 Handbook to the Birds of Australia. Sundevall's binomial name was followed as Lesson's 1829 record did not sufficiently describe the species; however, in 1911, the Australian amateur ornithologist Gregory Mathews pointed out that although Lesson's 1829 account did not describe the bird, his 1831 account did, and thus predated Sundevall by six years, and hence Sula dactylactra had priority. The American Ornithological Union followed in the 17th supplement to their checklist in 1920.
"Masked booby" has been designated the official common name by the International Ornithologists' Union (IOC). The species has also been called the masked gannet, blue-faced booby, white booby (for its plumage), and whistling booby (for its distinctive call). The Australian ornithologist Doug Dorward promoted the name "white booby" as he felt the blue coloration of its face was less prominent than that of the red-footed booby (Sula sula).
The masked booby is one of six species of booby in the genus Sula. A 2011 genetic study (depicted below) using both nuclear and mitochondrial DNA showed the masked and Nazca boobies (Sula granti) to be each other's closest relatives, their lineage diverging from a line that gave rise to the blue-footed (Sula nebouxii) and Peruvian boobies (Sula variegata). The masked and Nazca boobies were divergent enough to indicate that the latter, formerly regarded as a subspecies of the former, should be classified as a separate species. Molecular evidence suggests they most likely diverged between 0.8 and 1.1 million years ago. Complex water currents in the eastern Pacific may have established an environmental barrier leading to speciation. Subfossil bones 14,000 years old belonging to the species have been found in deposits on St. Helena Island.