Masked booby

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The Masked Booby, Sula dactylatra, is a large seabird of the gannet family, Sulidae. 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. Normally only one chick fledges.

This species breeds on islands in tropical oceans, except in the eastern Atlantic; in the eastern Pacific it is replaced by the Nazca Booby, Sula granti, which was formerly regarded as a race of Masked Booby.

There are four subspecies, none of which is separable at sea:

S. d. personata breeds in the central and western Pacific and off Australia
S. d. dactylatra breeds in the Caribbean and some Atlantic islands including Ascension Island. It has recently started breeding off Tobago, formerly being known in this area only from a single sight record from an oilrig off Trinidad.
S. d. melanops is the form breeding in the western Indian Ocean
S. d. tasmani (or S. d. fullagari) is the form breeding on Lord Howe and the Kermadec Islands. Prehistoric specimens known from the former and Norfolk Island are sometimes considered a distinct "species" (properly: subspecies). Since they were described first, in that case the extant population's name would be S. d. fullagari.

This species is fairly sedentary, 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 States. More remarkably, there have been three Western Palaearctic records of Masked Booby, presumably dactylatra, all from Spanish waters, although one of these also entered French territorial areas.

This is the largest booby, at 81-91 cm length, 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.

Masked Boobies are spectacular divers, plunging diagonally into the ocean at high speed. They mainly eat small fish, including flying fish.

References

BirdLife International (2004). [Sula dactylatra]. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 12 May 2006. Database entry includes justification for why this species is of least concern
Harrison. Seabirds. ISBN 0-7470-8028-8
Hilty. Birds of Venezuela. ISBN 0-7136-6418-5
ffrench, Robert (2003). Birds of Trinidad and Tobago. ISBN 0-7136-6759-1

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