A gregarious species, the brown booby forms nesting colonies on oceanic islands, which are usually small in size, but may number thousands of pairs when food is abundant. The brown booby feeds on squid and various fish species that live near the sea-surface, such as flying fish and anchovies. Foraging is frequently carried out alone or in small groups, by flying over inshore waters while searching for shoals of small fish driven to the surface by marine predators. At other times, however, large groups of brown boobies may gather on rocky cliffs and shorelines waiting for gulls to locate such shoals, before joining the large aggregation of feeding seabirds. Techniques used to catch prey include diving at a shallow angle and snatching prey from the surface, as well as steep plunge dives from up to 20 metres above the water surface, reaching prey over two metres below (3). Some individuals also snatch unwary fish while floating on the surface, or steal food from other seabirds (2) (3).
While the brown booby is a seasonal breeder in some areas, it generally breeds throughout year, with peaks in nesting activity occurring seasonally according to the colony location (2) (3). After securing a territory, often by fighting, the male brown booby advertises for a mate by holding its head and neck erect, bill pointing upwards, in a display known as sky-pointing. Interested females are then courted through behaviours such as mutual preening and bill touching. Once formed, breeding pairs may remain together for many years, continually reusing the same nesting site. Nests comprise a shallow depression in the ground, lined with marine flotsam, feathers and vegetation. A clutch of two eggs is laid asynchronously, and incubated by both parent birds for around 43 days, with the birds using the webbing of the feet to transfer heat to the developing eggs. In most cases, the second chick to hatch is eventually pushed out of the nest by the older, stronger chick, where it perishes; hence only one offspring is usually raised to fledging. The complete juvenile plumage is obtained at around 100 days, allowing the young bird to make its first flight, but parent birds continue to provide food for a further 30 to 260 days. The brown booby usually breeds at an age of four to five years, and may live for over 25 years (3).