Guide to North American Birds

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Adult and downy young. Photo: Mark Yokoyama/Flickr (CC BY NC ND 2.0)

Brown Booby

Sula leucogaster

Tropical seas around the world are home to this large, long-winged, strong-flying seabird. In North America it is seen most often near the Dry Tortugas, Florida, where it perches in trees or on navigational markers. It may have nested on the Florida Keys in the past, but the only United States nesting sites today are in Hawaii.

Conservation status	Vulnerable to disturbance on islands where it breeds, but survival probably ensured by wide range and large number of nesting sites.
Family	Boobies and Gannets
Habitat	Tropical oceans. Widespread at sea, including very far from land, over warm waters in tropics and subtropics. Also often found close to shore, especially around islands, sometimes foraging in very shallow or muddy waters. Nests on rocky or sandy islands.

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Feeding Behavior

Forages mostly by plunging headfirst into water from flight, usually diving at angle and from fairly low above surface. Sometimes hovers before diving, dives from perch, swoops low to take items from surface, or seizes items while swimming. May pursue flying fish in the air. Also steals food from other birds.

Eggs

1-2, rarely 3. Whitish to pale blue-green, becoming nest-stained brown. Incubation is by both sexes, 40-47 days. Young: Both parents feed young, by regurgitation. When 2 eggs laid, 2nd young to hatch rarely survives. Period from hatching to first flight varies, depending on food supply, 84-119 days. Juvenile returns to nest site and begs to be fed for many weeks after first flight, often 20 weeks or more.

Young

Both parents feed young, by regurgitation. When 2 eggs laid, 2nd young to hatch rarely survives. Period from hatching to first flight varies, depending on food supply, 84-119 days. Juvenile returns to nest site and begs to be fed for many weeks after first flight, often 20 weeks or more.

Diet

Mostly fish. In North American waters, diet includes flying fish and mullet, also squid and shrimp.

Nesting

Probably first breeds at age of 4 years, and may mate for life. Courtship displays by members of pair include bill-touching, bowing, throwing head back with bill pointing skyward. Nests in large or small colonies, sometimes isolated pairs, on tropical or subtropical islands. Nest: Site is on ground or cliff. Nest is shallow depression, sometimes sparsely lined, sometimes with large mound of twigs, grass, and debris, built by both sexes.

Illustration © David Allen Sibley.
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Text © Kenn Kaufman, adapted from
Lives of North American Birds

Migration

Present year-round in most parts of range, with only local wandering at sea. Birds from western Mexico sometimes stray north into interior of American southwest (especially Salton Sea, Colorado River).