Birds of Midway Atoll
Masked Booby / Sula dactylatra
Masked Boobies nest in small numbers at Midway and no historical information indicates that they were previously more numerous. There are generally less than five nesting attempts per year.
Feeds by plunging head first into the water from the air, sometimes diving from as high as 30m. Feeding areas are usually many miles from land. Feeds primarily on fish and squid. Feeding birds are often associated with schools of large predatory fish, such as tuna. Feeding generally occurs during daylight hours.
Breeding season occurs between February and August. Breeds colonially. Nests are located on the ground and consist simply of a shallow depression. Begins breeding at four years of age. Monogamous. Two chalky white eggs are layed. Lacks brood patch and instead incubates with feet. Parents share incubation duties. Average incubation shift is 9.5 hours. Incubation period averages 43 days. Siblicide exhibited by chicks. The first egg hatches four to nine 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 once or twice a day. Fledging occurs 109-151 days after hatching. Post fledging care and feeding continues for one to two months.