Skip Navigation

Brown Booby

Sula leucogaster
Brown boobies

Adults are chocolate brown with white underwing coverts and belly. Sexes are distinguishable by face, bill, and leg color. These parts are yellow in females and are grayish green in males, which in addition, have a bluish throat. Juveniles have plumage similar to adults except that belly and under wing covert color is light brown.

Breeding season occurs between March and November. Nests are located on the ground and consist of a shallow depression surrounded by twigs or other vegetation. An average of two chalky white eggs are laid. Brown boobies lack a brood patch and instead incubate with their feet. Parents share incubation duties and the average incubation shift is 12 hours, with an average incubation period of 43 days. The first egg hatches several days before the second and the first chick to hatch ejects the second chick from the nest shortly after it emerges from the egg. Chick feeding occurs on average once every 17 hours. Fledging occurs 85-103 days after hatching. Post-fledging care and feeding continues for one to two months.

Brown boobies were considered the most common booby at Midway in the 1930s. Currently they are uncommon at the atoll. Rats (Rattus rattus), which have now been eradicated from Midway, are implicated in their decline. In late 1999, the first nest since 1963 was recorded. 

Facts About Brown Booby

Diet
Daytime surface feeders – primarily flying fish eggs. They rely on flying fish eggs, which are easier to locate during the day. They also feed on squid and crustaceans. Unlike the Laysan albatross, whose retinas possess a high level of rhodopsin enabling better night vision, the black-foots have limited nocturnal vision.
Life Span
12-40 years
Size
Length: 64-74 cm 25.6.6-29.6 in); wingspan: 193-216 cm (6-7 ft) 
Last Updated: May 13, 2013
Return to main navigation