Brown Booby: where and when to see them

The brown booby is a powerful tropical seabird often seen commuting between island colonies and offshore feeding grounds. Adults have chocolate-brown upperparts and a sharply contrasting white belly. Females are generally larger than males, while bare-part colours also differ. Recent taxonomy separates the eastern Pacific Cocos booby from brown booby in some major lists, an important distinction for Costa Rica and eastern Polynesia that older wildlife catalogs may not reflect consistently.

Size

64-76 cm long

Weight

0.9-1.5 kg

Lifespan

Not reliably established

Status

Check current assessment

Brown boobies search for prey from the air and plunge into the sea when they locate fish. They may feed in loose groups where predatory fish concentrate prey near the surface. On land, pairs use courtship displays involving the bill, head and wings, then occupy open ground nests. Adults alternate incubation and chick care. Birds can appear remarkably unwary at colonies, but close human approaches may expose eggs or chicks to heat and predators. Pairs maintain strong pair bonds and often return to the same nest site year after year. Chicks are semi-altricial, hatching with sparse down and requiring extensive parental care. While foraging, they employ dynamic soaring, utilizing wind currents to conserve energy during flight.

• Females are typically larger than males.
• All four toes are connected by webbing.
• A clutch often contains two eggs, but usually only one chick survives.
• Eastern Pacific birds formerly included here may now be classified as Cocos boobies.

There is no single breeding season across this wide tropical range. Dry-season travel can improve comfort at coastal viewpoints, while colony attendance follows local conditions. Check regional taxonomy and current colony information, especially in the eastern Pacific, before interpreting older records as evidence for this species. Peak breeding activity in some regions coincides with periods of higher ocean productivity. Monitoring local seabird reports and specific island conservation group updates can provide the most current breeding information. Coastal upwellings or current convergences often concentrate prey, influencing booby presence.

Tropical and subtropical seas provide feeding habitat, particularly around islands, continental shelves and productive current boundaries. Colonies occupy rocky islets, cliffs and open ground on islands. Roosting birds may use navigation structures, but nesting habitat generally needs limited disturbance and relatively safe access to the sea. They are widely distributed throughout tropical and subtropical oceans globally, rarely straying far from land. While nesting, they prefer remote islands and cays to avoid land-based predators. During non-breeding periods, individuals may range more widely across open ocean waters.

Flying fish, other small schooling fish and squid are important prey. Birds capture food through aerial plunges and short submerged pursuits. Feeding sometimes occurs near tuna or other predatory fish, while fishing activity can attract birds but also expose them to hooks and entanglement. They typically hunt within 50 km of their nesting colonies or roosting sites. While primarily feeding on small fish, they are also known to take discards from fishing vessels. This species typically hunts alone or in small groups, less commonly forming large feeding frenzies.

Common name

Brown Booby

Scientific name

Sula leucogaster

Animal group

Birds

Size

64-76 cm long

Weight

0.9-1.5 kg

Lifespan

Not reliably established

Status

Check current assessment

Identification

Adults differ from masked boobies in their dark head and chest, but separation from the recently split Cocos booby requires geographic context and careful attention to sex-specific head coloration. Juveniles are generally browner overall with a paler belly, lacking the sharp contrast of adults. Sexes are outwardly similar, but females are typically slightly larger than males. The bill is sharp and pointed, often greenish-yellow in males and duller yellow or bluish in females.