Group Title: United States Virgin Islands animal fact sheets
Title: Brown booby
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 Material Information
Title: Brown booby
Series Title: United States Virgin Islands animal fact sheets
Physical Description: Book
Language: English
Creator: Division of Fish and Wildlife, Department of Planning and Natural Resources, United States Virgin Islands
Publisher: Division of Fish and Wildlife, Department of Planning and Natural Resources, United States Virgin Islands
Place of Publication: St. Thomas, VI
 Record Information
Bibliographic ID: UF00093446
Volume ID: VID00006
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.


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Department of Planning and Natural Resources
Division of Fish and Wildlife
U.S.V.I. Animal Fact Sheet #06

Brown Booby
Sula leucogaster

Kingdom Anamalia
Phylum Chordata
Subphylum Vertebrata
Class Aves
Order -- Pelecaniformes
Family Sulidae
Genus Sula
species leucogaster
Identification Characteristics
+ Body Length 64-74 cm
+ Weight 725-1500 g
+ Wing span 130-150 cm
+ Dark head, breast, mantle, and tail
+ White belly cleanly separated from dark breast
+ Underwings white with dark border
+ Large, yellow or greenish, pointed bill
+ Yellow legs and feet

The Brown Booby is a medium-large seabird
characterized by dark brown coloration except on
the breast, abdomen and underwing, which are
white in the adult. Immatures are entirely dusky
brown. Females are larger than males, but in the
Virgin Islands sexes can be distinguished by bill
color (pinkish-yellow in females, greenish-yellow in
males) and vocalizations (females honk, males
whistle). The genus Sula is from the Icelandic word
Sulan, meaning "an awkward fellow". The name
"booby" comes from the Spanish word bobo, which
means "stupid fellow" referring to the bird's lack of
fear of man and clumsiness on land making them
easy to catch. Although awkward on land, their
cigar-shaped bodies and narrow wings reflect a
superb aerodynamic design, which is specially
adapted for plunge-diving. Their dagger-shaped bill
is long and pointed with serrated edges, ideal for
swift seizure and grasping of slippery fish. The
external nostrils are closed, but secondary nostrils
beside the mouth are covered by moveable flaps
when the bird plunge-dives into the sea. A semi-
transparent third eyelid closes to protect the eyes in

bad weather and underwater. The feet are
totipalmate (webbed between all four toes) to help
the birds to swim well. They have strong skulls and
rib cages to withstand the pressure of diving into the
water. Air sacs under the skin also help to cushion
the blow when diving for fish.

Distribution & Habitat
The race leucogaster is distributed over the tropical
Atlantic, the Caribbean and the Gulf of Mexico. In
the Virgin Islands, the Brown Booby is present year
round and is the most common and widely
distributed of the three booby species that occur in
this region. Approximately 600-1000 breeding pairs
are distributed on five offshore cays (small islands)
which are government-owned and declared Wildlife
Sanctuaries. These islands are difficult to access
and are uninhabited with vegetation generally
characterized as subtropical dry forest. Nesting
habitats preferred by Brown Boobies are grassy
flats or slopes. Data from banding studies show that
very little inter-colony movement occurs. The total
breeding population in 1996 dropped dramatically
as a result of Hurricane Marilyn, but numbers have
slowly risen since then.

Food and Feeding
Brown Boobies are primarily inshore feeders. In
the Virgin Islands, they feed on flying fish, squid,
and a variety of smaller baitfish. Boobies are
powerful high-speed soaring birds that can torpedo
after a flying fish or fall straight down like a falcon.
Seabirds have the ability to drink salt water by
using a specialized salt gland located behind the
orbit of the eye. The salt gland allows the booby to
excrete excess salt through the nasal passages which
is eliminated by shaking the head. Feeding
aggregations of boobies are of considerable
economic importance to sport and commercial
fishermen as beacons for locating pelagic fish

All seabirds must return to land to breed. Like most
seabirds, boobies are characterized by long
lifespans (20 years or more), low reproductive rates,
slow chick growth and delayed maturity. In the
Virgin Islands, nesting can occur during any time of
the year, but typically two peaks occur; one during
fall-winter and a second peak in March-April. The
five breeding colonies in the Virgin Islands may not
be synchronous. Brown Booby nests are placed on
the ground and are constructed of grasses and
occasionally seaweed. Like the Masked Booby,
Brown Boobies usually lay two eggs but raise only
one chick to maturity. Incubation begins when the
first egg is laid, resulting in the first chick being
considerably larger and stronger than the second. It
is for this reason that the second smaller chick is
usually the one that does not survive. Both sexes
take turns incubating the eggs and caring for the
young chick. Incubation lasts about 42 days and
because brood patches are absent, boobies use the
webs of their feet, which are extensively
vascularized, to transmit essential heat to the eggs.
Once hatched, chicks take about 100 days to fledge
(a bird capable of flight) and are fed an additional 6
weeks at the nest site by the parents. Boobies feed
their young directly from the adult's throat. A 3-
year study of Brown Booby nesting success in the
USVI found that only 21% of nests produced a
fledged chick. Those chicks that survive spend
several years away from the colony before
returning, usually to the colony of their birth, to
breed. Juvenile boobies banded in the USVI have
been recovered from Bermuda, Jamaica, Belize and

Like most natural resources, seabirds have been
exploited by humans. The Brown Booby especially
has suffered because of human activity and many
islands have lost much of their populations through
the harvesting of eggs and chicks for food, by
military activity, the introduction of pests, the
occurrence of oil spills, over-fishing that reduces
available food for the birds, entanglement in fishing
gear and habitat destruction. Few colonies are
effectively protected and human exploitation is still
quite severe.

What you can do to help
* All government owned cays have been posted
with Wildlife Sanctuary signs to protect major
seabird colonies. Entry to most of the cays is
prohibited to reduce disturbance to nesting seabirds.
Persons entering breeding colonies may cause
reduced nesting success or colony abandonment by
causing adults to fly off their nests, leaving eggs or
small young vulnerable to predators. Chicks are
born naked and helpless and can die in a matter of
minutes due to heat stress if not shaded by the
parent. Please report any unauthorized entry into a
seabird colony to Environmental Enforcement (774-
3320) or the DFW (775-6762).
* A major cause of injury and death to many
seabirds in the Virgin Islands is the fishhook and
monofilament line. If you catch a bird on your
fishing line, DO NOT CUT THE LINE. The bird
will trail this line back to the nesting colony,
possibly entangling more birds, and will die a slow
torturous death. Please slowly reel in the bird
and if possible gently land the bird with a hand net.
The bird will be calmer if its head is covered and
this affords some protection to the handler from its
sharp bill. Cut off the barbed end of the hook then
back the hook out. If the bird has swallowed the
hook or you are unable to dislodge it, please bring
the bird to a local veterinarian or to DFW.

By William Coles and Judy Pierce, 2003
ST. THOMAS, VI 00802
PHONE 340-775-6762 FAX 340-775-3972
PHONE 340-772-1955 FAX 340-772-3227

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