Brown Booby Identification Guide

Key Field Marks

• Large, cigar-shaped seabird around 71–79 cm long with long, pointed wings and a wedge-shaped tail.
• Adult: solid chocolate-brown head, neck, back, and upper breast that end in a sharp, clean line against a bright white lower breast, belly, and underwing coverts — this crisp "bib" boundary is the single best field mark.
• Bill is long, stout, and dagger-like; yellow in females, duller yellow-green or grayish in males; feet are yellow.
• Juvenile: more uniformly grayish-brown overall with a less crisply demarcated, duskier belly.

Separating It From Similar Species

• Masked Booby: white body with a black facial mask and black flight feathers/tail, no brown bib.
• Red-footed Booby: bright red feet and a blue-based bill; occurs in white, brown, and intermediate color morphs, but even brown-morph birds lack the sharply cut brown-to-white breast boundary of Brown Booby.
• Northern Gannet (rare overlap in range): much larger, white-bodied with a golden-buff head wash and black wingtips, not brown-bodied.
• The clean-edged brown bib against a white belly is unique among boobies found in North American waters.

Habitat, Range & Season

• Widespread on tropical and subtropical islands and coastlines worldwide; in North American waters found around Florida, the Gulf Coast, and increasingly off California and Texas, especially in summer and fall.
• Nests colonially on remote islands and cays; frequently roosts on offshore buoys, channel markers, and boats.
• Feeds by plunge-diving from moderate heights for fish and squid, often near the surface, and readily follows boats.

Voice

• Largely silent away from breeding colonies.
• At colonies, gives harsh honking, quacking, and grunting calls; males tend to have thinner, more whistled calls than the deeper honks of females.