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These aerial acrobats, often called Man o’-war birds, have an ill-deserved reputation as full-time pirates because they are often seen chasing other seabird species, particularly boobies, to commandeer a meal. Hanging in the air near a nesting colony, a frigatebird lies in wait for an unsuspecting seabird returning to the colony to feed its chick. With great aerial dexterity, it pursues the returning seabird, sometimes even grabbing its tail-feathers. Eventually the victim regurgitates its meal, whereupon the adept frigatebird darts down, catching the fish before it hits the water. The name “frigatebird” was inspired by the resemblance of this behavior to the actions of the fast, maneuverable frigates, or man-o’-war ships, used by pirates centuries ago. The Hawaiian name for the species, “‘Iwa,” also means “thief.” But, in fact, frigatebirds catch the majority of their meals without stealing them. They fly along waiting for a flying fish to break the ocean surface, or catch fish and squid that are swimming within several centimeters below the surface.
The Great Frigatebird is highly specialized for an aerial life, having a greater ratio of wing area to body mass than any other bird, a deeply forked tail for agile maneuvering, and very small legs and feet (which make walking impractical). It is among the few seabirds that are sexually dimorphic in plumage as well as in size. Both males and females have a gular sac, analogous to that of the pelican, but only the male inflates the sac into a bright-red balloon. He does this to attract a female during courtship: Groups of males sit in bushes, gular sacs inflated, whinnying, and wing-waving at females flying overhead. Once a nest is built and incubation is proceeding, the male’s gular sac gradually deflates and disappears into the throat-feathers. Both sexes provide parental care during the long incubation period and exceptionally long chick-rearing period. As is characteristic of many tropical seabirds, frigatebirds have a long life span (30–40 years), exhibit deferred maturity, lay only 1 egg, and have a very slow-growing chick.
The Great Frigatebird is pantropical (between about 25°N and 25°S), nesting in colonies on islands from the Western Atlantic Ocean throughout the Pacific (including the Hawaiian Archipelago; Fig. 1) and Southern Indian Oceans. It is not found in the Caribbean.
There are few data on the migration range of this species, but it is thought to spread out from breeding colonies and inhabit a much broader area of the ocean when not nesting. Its numbers have declined since humans began inhabiting its range—building on nesting islands and taking frigatebirds for food. Great Frigatebird populations that remain generally nest in remote areas and have been little studied by scientists. Many areas of the biology of this species are in need of study.