State recognized as Indigenous Nature
Serve Heritage Rank G5 – Secure
North American Waterbird Conservation Plan – Moderate concern
Regional Seabird Conservation Plan - USFWS 2005
There are four brown booby subspecies and have a pantropical distribution. It is a large, striking seabird and of the four brown booby species, there is one that resides in Hawaiʻi. Their hawaiian name, ʻā, is the same name shared with other hawaiian booby congeners--the Masked Booby and the Red-footed Booby--due to their similar body characteristics such as beak, feet, tail, and relative size.
Individuals have long pointed wings and a relatively short, wedge-shaped tail. Adult male and female are overall dark brown with a white belly and underwings along with a sharp demarcation across the lower breast between the white belly and brown of their neck. They also have a large bill with yellow legs and feet for females, and grayish-green in males; females are larger than males.
Brown booby generally forage in nearshore waters and captures prey by plunge-diving from 50 meters above water, usually remaining underwater for about half a minute. While some are observed foraging alone, most forage in large, mixed species flocks associated with schools of large predatory fish that drive prey species to the surface. Their diet is comprised of flying fish, squid, mackerel scad, juvenile goatfish, and anchovy.
Most return to their natal colony to breed and usually nest in small colonies of tens of hundreds of pairs. As one of the only two ground-nesting booby species—the other is the Masked Booby (Sula dactylatra)—it is the only one that builds a nest as the construction is an important part of courtship. Nests are constructed from whatever is available including branches, seabird bones, and human debris.
Contrary to the Red-Footed Booby nesting, both the Masked Booby and Brown Booby typically lay two eggs per breeding season. The eggs hatch asynchronously, and the first chick to hatch usually pushes the other sibling out of the nest. Peak egg laying occurs between March and May and chicks fledge by September. Both parents incubate eggs and brood and feed chicks. Adults continue to feed young up to 37 weeks after fledging. Birds first breed at four to five years of age and the oldest known individual was 26 years old.
Distribution & Abundance
‘Ā (brown booby) are residents of NWHI as well as on the offshore isles of the main Hawaiian Islands such as, for example, Moku Manu, Lehua and possibly on the island of O‘ahu on the cliffs of Ulupa‘u Head at the Kāne‘ohe Bay Marine Corps Base.
Location & Habitat
On Kure, they can usually be find them perched off the ground when not nesting in the interior sections of the atoll where there is open ground.