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"Parasula" redirects here. The fossil genus established by C.J.O. Harrison is properly called Empheresula.


On nest


The Masked Booby, Sula dactylatra, is a large seabird of the gannet family, Sulidae. This species breeds on islands in tropical oceans, except in the eastern Atlanticmarker; in the eastern Pacific it is replaced by the Nazca Booby, Sula granti, which was formerly regarded as a subspecies of Masked Booby (Pitman & Jehl 1998, Friesen et al. 2002).

A conspicuous and distinct gannet-like species, it was proposed for separation in a monotypic subgenus Pseudosula, but the Nazca Booby and as it seems also the Brown Booby (S. leucogaster) is a quite close relative.

Classification

First described by French naturalist René-Primevère Lesson in 1831, the Masked Booby is one of five species of booby in the genus Sula. The Nazca Booby (S. granti) was formerly regarded as a subspecies. There are four subspecies, none of which is separable at sea:

  • S. d. personata van Tets, Meredith, Fullagar & Davidson, 1988: Austropacific Masked Booby
Breeds in the central and western Pacificmarker and around Australia, as well as off Mexicomarker and on Clipperton Islandmarker. Birds of the latter two locations have been separated as subspecies granti, and the NW Australian population has been named as subspecies bedouti, but neither is usually considered valid.


  • S. d. dactylatra van Tets, Meredith, Fullagar & Davidson, 1988: Atlantic Masked Booby
Breeds in the Caribbeanmarker and some Atlantic islands including Ascension Islandmarker. It has recently started breeding off Tobagomarker, formerly being known in this area only from a single sight record from an oil rig off Trinidadmarker.


  • S. d. melanops van Tets, Meredith, Fullagar & Davidson, 1988: Western Indian Ocean Masked Booby
Breeds in the western Indian Oceanmarker.


  • S. d. tasmani (including S. d. fullagari) van Tets, Meredith, Fullagar & Davidson, 1988: Tasman Booby or Lord Howe Masked Booby
The form breeding on Lord Howemarker and the Kermadec Islandsmarker. Large prehistoric specimens known from the former and Norfolk Islandmarker are sometimes considered a distinct "species" (properly: subspecies). If this is correct, the extant population's name would be S. d. tasmani as S. d. fullagari was described after Sula tasmani. Comparison of ancient DNA form tasmani specimens and living fullagari indicates that they are not distinct.


Description

This is the largest booby, at 81-91 cm long, and with a 152 cm wingspan and 1500 g weight. Adults are white with pointed black wings, a pointed black tail, and a dark grey facemask. The sexes are similar, but the male has a yellow bill, and the female's is greenish yellow; during the breeding season they have a patch of bare, bluish skin at the base of the bill. Juveniles are brownish on the head and upperparts, with a whitish rump and neck collar. The underparts are white. Adult plumage is acquired over two years.

The Masked Booby is silent at sea, but has a reedy whistling greeting call at the nesting colonies. While on the breeding grounds, these birds display a wide range of hissing and quacking notes.

Behaviour

Masked Boobies are spectacular divers, plunging diagonally into the ocean at high speed. They mainly eat small fish, including flying fish. This is a fairly sedentary bird, wintering at sea, but rarely seen far away from the breeding colonies. However, Caribbean birds occasionally wander north to warm southern Gulf Stream waters off the eastern seaboard of the United Statesmarker. More remarkably, there have been three Western Palaearctic records of Masked Booby, presumably dactylatra, all from Spanishmarker waters, although one of these also entered Frenchmarker territorial areas.

Breeding

It nests in small colonies, laying two chalky white eggs on sandy beaches in shallow depressions, which are incubated by both adults for 45 days. In most cases, the first chick will kill its smaller, weaker sibling after it hatches. Siblicide has been well studied in this species; researchers such as David Anderson have demonstrated that while the boobies can manage to feed two chicks if siblicide is prevented, they do so at a steep penalty to health and future reproductive success.

References

Adult in flight, Galapagos Islands


  1. Mack, Alison. 1997. "Natural born killers." Earth 6, no. 3: 12. General Science Collection, EBSCOhost (accessed May 4, 2007).
  2. Anderson, David J. 1990. "Evaluation of Obligate Suicide in Boobies. 1. A Test of the Insurance-Egg Hypothesis." The American Naturalist 135, vol. 3: 334-350
  3. Anderson, David J. 1990. "Evolution of Obligate Siblicide in Boobies. 2: Food Limitation and Parent-Offspring Conflict" Evolution 44 no. 8: 2069-2082
  4. Alda, Alan (Host). (1999). Voyage to the Galapagos [Television series episode]. Scientific American Frontiers. Arlington, Virginia: Public Broadcasting Service. (transcript here: http://www.pbs.org/saf/transcripts/transcript1001.htm)


  • Database entry includes justification for why this species is of least concern


  • Bull, John L.; Farrand, John Jr.; Rayfield, Susan & National Audubon Societymarker (1977): The Audubon Society field guide to North American birds, Eastern Region. Alfred A. Knopf, New York. ISBN 0-394-41405-5




  • Friesen, V. L.; Anderson, D. J.; Steeves, T. E.; Jones, H. & Schreiber, E. A. (2002): Molecular Support for Species Status of the Nazca Booby (Sula granti). Auk 119(3): 820–826. [English with Spanish abstract] DOI: 10.1642/0004-8038(2002)119[0820:MSFSSO]2.0.CO;2 PDF fulltext


  • Harrison, Peter (1988): Seabirds (2nd ed.). Christopher Helm, London. ISBN 0-7470-1410-8


  • Hilty, Steven L. (2003): Birds of Venezuela. Christopher Helm, London. ISBN 0-7136-6418-5


  • Pitman, R. L.; Jehl, J. R. (1998): Geographic variation and reassessment of species limits in the "Masked" Boobies of the eastern Pacific Ocean. Wilson Bulletin 110(2): 155-170.



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