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Masked Booby Sula dactylatra dactylatra 


Masked Boobies

At a glance

The largest and rarest of the tropical boobies

Declining in the region

Most colonies are small (2-25 pairs)

Available research based mostly on populations from outside the region

Index

Identification:

Largest (32-36 inches, 81-92 cm, total length) of the tropical boobies. Can live to 30 years or more. Female’s mass greater than male’s.

Adults

White with black in tail, primaries and scapulars. Adults superficially resemble Northern Gannets, but adult Gannets have yellow-hue on back of head and neck. Black tips of long scapulars make the black wing stripe extend evenly from primaries to base of the wing. Gannets lack the black tips on scapulars, making the wingstripe lose width as it nears the body. White-phased Red-footed Boobies are much smaller and have a distinctive smudge of black feathers on the wrist in the underwing and lack the black scapulars on the upper wing.

Juveniles

Immature and juvenile Masked boobies have white under-parts, and a white collar. Juveniles are brown and resemble Brown Boobies, but the brown is on the head and neck and does not extend onto the breast as in Brown Booby. Underwing pattern has a thin brown stripe from 'armpit' to 'hand' bordered in white both anteriorly and poseriorly. Juvenile Brown Booby has brown borders to the underwing with a short, thin stripe from the 'hand' that fades out before it reaches the body.

Alternative names:

English: White Booby, Blue-faced Booby

French: Fou Masque

Spanish: Piquero enmascarado.

Systematics

Nine species in genus Sula including 3 gannets and 6 boobies. Gannets are temperate to boreal; the boobies are primarily tropical. Four to seven subspecies of Masked Booby are recognized depending on the authority. Differences based on overall size and coloration of soft parts. Western Atlantic subspecies is endemic to West Indies and Gulf of Mexico and is the smallest of the named races. Has a straw colored bill and orange to olive colored legs and feet.

Likely locations

At and near breeding sites, because of rarity and wide marine dispersal seldom encountered at sea.

Distribution

Rare, pan-tropical species; various subspecies occur throughout the world. While this is the least common species of booby, it is one most encountered at sea as they disperse great distances from their breeding grounds. Occurs northward in the Gulf Stream to the Carolinas, where it is a deep water, pelagic species usually associated with Sargassum.

Masked Booby Distribution

Biology

At sea

Plunge diver, diving from heights of up to 30 m. Mostly diurnal but some feeding occurs at night. Feed on flying fish, jacks and squid. Known to forage 65 km from breeding colonies, and dispersing further from nesting sites than other boobies. Spends considerably portion of the day resting of surface or perched on floating debris.

At the nest

Nest on remote islands lacking mammalian predators, often in association with other species of boobies. Colonies are typically on flat unforested islands. Nest on the ground but do not construct actual nests. Eggs blue but covered with white chalky layer. Like other boobies they often lay more than one egg (typically two) but only one chick is raised. Incubation 38-49 days, fledge at 109-151 days but young return to nesting area to be fed by parents until 139-180 days of age.

Current Population

A total of 580-650 pairs in 26 known colonies in West Indies. At least five colonies in the region have been extirpated in the historic period, and, based in pre-Columbian middens, several others were lost prior to European contact.  The vast majority of the Masked Boobies in this population nest outside the Caribbean, with 3863 pairs on islands of the Campeche Bank in the Gulf of Mexico.

Location

Colonies Low Estimate
Bahamas 1 0
Florida Keys15
Cayman Islands 1 0
Jamaica 2 114
Puerto Rico 3 105
US Virgin Islands 2 80
Anguilla 2 62
Antigua and Barbuda 1 0
St. Vincent and the Grenadines 1 0
Grenada 1 1
Trinidad and Tobago 1 4
Venezuela 7 213
Colombia 2 0
Honduras 1 0?
Mexico (Numbers from 1986) 4 3863
Total 31 4384

Conservation Status 

This is the least common booby and one of the rarest birds in the Atlantic. In the West Indies proper, one-fifth of the breeding pairs use a single island off Jamaica that they share with several hundred fishermen. The southern Caribbean population is vulnerable to a number of factors. Rarely recolonize once populations are extirpated. Considered endangered in region (Schreiber and Lee 2000; Bradely and Norton, 2009). Status of the huge Campeche Bank population has not been confirmed since the 1980's.

Conservation Needs

Can coexist with carefully regulated ecotourism but is not established on islands near any tourist centers. Pacific populations have been rapidly exterminated by feral pigs and have shown dramatic recoveries when pigs are removed. Feeding behavior at sea suggest this would be a prime candidate for pelagic fishery by-catch. Rarity of the species and confusion with gannets probably results lack of reporting of this booby as a by-catch species.

The larger more important colonies need monitoring and protection, and should be off limits to random visits by boaters, tourists and sea bird biologists. Agencies granting permits for research on cays supporting booby colonies need to check the credentials and experience of the applicants.

A region-wide survey of all historic nesting sites is needed during the breeding season. These sites should also be monitored for introduced mammals. Local education, informative posted signs, and enforcement needed for all known colonies.  Active colonies need to be checked 3-4 times a year to determine breeding success at specific sites and to identify problems. Because boobies are long lived the presence of a number of adult birds in a colony does not necessarily indicate successful breeding. Banding studies to document the amount of movement and exchange of birds between colonies is needed. DNA analysis would be useful to compare populations within the West Indies to those nesting along the Central American and South American coasts.

Photos

Selected References:

Anderson, D. A. 1993. Masked Booby (Sula dactylatra). In The Birds of North America. No. 73 (A. Poole and F. Gill, Eds.). Philadelphia: The Academy of Natural Sciences; Waashington, D.C.: The American Ornithologists’ Union.

Clapp, R. B. and W. B. Robertson, Jr. 1986. Nesting of the Masked Booby (Sula dactylatra, new record) on the Dry Tortugas, Florida: The first record for the contiguous USA. Colonial Waterbirds 9:113-116.

Schreiber, E. A. 2000. Status of Red-footed, Brown and Masked Boobies in the West Indies Pages 46-57 in E. A. Schreiber and D. S. Lee (eds.) Status and Conservation of West Indian Seabirds. Society of Caribbean Ornithology, Special Publication Number 1. 225 pp.

Tunnell, J. W. and B. R. Chapman. 2000. Seabirds of the Campeche Bank Islands, Southeastern Gulf of Mexico. Atoll Research Bulletin 482:1-50. 

West Indian Breeding Seabird Atlas by Will Mackin and David Lee is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License.Based on work at www.wicbirds.net.Permissions beyond the scope of this license may be available at www.wicbirds.net.

Suggested Citation: Lee, D. S., W. A. Mackin. 2009. Masked Booby. West Indian Breeding Seabird Atlas <http://www.wicbirds.net/mabo.html>. Last Updated: _____. Date accessed: ______.

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March 31, 2009
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