Midway Atoll National Wildlife Refuge
Pacific Region
 

Birds of Midway Atoll

Brown Booby / Sula leucogaster

Photo of brown booby Description

Adults chocolate brown with white underwing coverts and belly. Sexes 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. Length: 71-76cm (28-30 in); wingspan: 137-145 cm (54-57 in); life span: max. known age 16 years.

 
Brown Booby
Photo credit: Ken Neithammer/USFWS

Midway Population

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.

Feeding Habits

Feeds by plunging head first into the water from the air. Usually forages near shore, often within 80 km of breeding grounds. Solitary feeder. Primary prey item is flying fish. Feeding generally occurs during daylight hours.

Breeding

Breeding season occurs between March and November. Breeds colonially. 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 layed. Lacks brood patch and instead incubates with feet. Parents share incubation duties. Average incubation shift is 12 hours. Incubation period averages 43 days. Siblicide exhibited by chicks. The first egg hatches several days before the second. 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.

Last updated: May 21, 2009