The brown booby (Sula leucogaster) is a large seabird of the booby family, Sulidae, of which it is perhaps the most common and widespread species. It has a pantropical range, which overlaps with that of other booby species. The gregarious brown booby commutes and forages at low height over inshore waters. Flocks plunge-dive to take small fish, especially when these are driven near the surface by their predators. They only nest on the ground, and roost on solid objects rather than the water surface. The booby's head and upper body (back) is covered in dark brown to black plumage, with the remainder (belly) being a contrasting white. The bare part colours vary geographically, but not seasonally. The species also displays sexual dimorphism of the bare part colours, the males having a blue orbital ring, as opposed to the yellow orbital ring of the female. In addition the male of subspecies S. l. brewsteri is distinctly plumaged in having the forehead, forecrown and chin white, merging to a greyish brown neck and breast.
The Brown Booby occurs through the tropical and subtropical oceans of the world (Raffaele and others 1998). It is a fairly common resident in Puerto Rico (Raffaele and others 1998), especially in the far eastern and western coasts (Oberle 2018), and a fairly common non- breeding resident on Vieques from December to May but uncommon to rare at other times of the year (Gemmill 2015). This seabird is generally seen in rocky cays, on islets, and out at sea. It has a large breeding colony on Mona (Raffaele 1989a), although the largest colonies are currently found in La Cordillera Natural Reserve between Fajardo and Culebra (Oberle 2018), while the large colony on Desecheo was eliminated shortly after the introduction of rhesus monkeys (Macaca mulatta) (Oberle 2018). The atlas fieldwork yielded a total of 93 records within 52 hexagons or 11 percent of the 479 total hexagons (see map). Of the 52 hexagons where this species was found, breeding met the atlas definition of confirmed in 17 percent (9) of the hexagons and possible in 10 percent (5), while the species was observed in 73 percent (38) of the hexagons but without evidence of breeding (see map). Brown Booby distribution. The map shows the highest breeding code by hexagon and overlaying the ecological life zones in Puerto Rico. Note: percentages may not total 100 due to rounding. 139Brown Booby/Boba Parda
This species usually nests on the ground on remote islands or inaccessible sea cliffs, and breeding season peaks from March to June and from September to October, according to previously published reports (Raffaele and others 1998). Atlas results show that the Brown Boobys breeding activity peaks in July (see chart). Results show that the Brown Booby breeds within the subtropical dry forest life zone (100 percent of the hexagons) in associated islands and cays around Puerto Rico including Culebra, Mona and Monito, Desecheo, and Arrecifes de La Cordillera (see table and map).
The Brown Booby is listed as a species of least concern by the IUCN (BirdLife International 2018), while locally this species is not listed in any of the threatened categories used by PRDNER and USFWS. In Puerto Rico, the Brown Booby has a protected habitat in land of 17 percent or 57 km2 of the total area covered by the hexagons where evidence of breeding was found for this species (336 km2).