Fregatidae: Frigatebirds
The frigatebirds are a small, uniform family of large, lanky, aerial seabirds that soar high over the tropical oceans and live by a combination of piracy and direct predation on jumping fish (especially flying fish). Frigatebirds are named for their strategy of stealing from other fishing seabirds, especially boobies: harassing and attacking them in flight, pressuring them to disgorge, then swooping down to snag the food before it hits the water.
Males of all species have a bright-red pouch of bare skin on the throat and neck which they inflate like large balloons during courtship displays. During territorial fights, males often attack and sometimes puncture one another’s inflated pouches.
Peculiarly, although they are exclusively oceanic, frigatebirds are incompetent in water. Despite being masters of the marine airspace, they must return to dry land to roost.
Identification
Frigatebirds are notoriously difficult to identify, as the differences between species are generally less pronounced than the differences among plumages within species, which vary by sex and age. Adult male plumages are mostly similar, females are somewhat more distinctive, and the many immature plumage stages are both variable and confusing. In much of the world only one or two species occur regularly, so identification is often based primarily on geography and probability.
Taxonomy
The species-level taxonomy of the Fregatidae has traditionally been regarded stable, with five recognized species, of which two are highly localized, two are pantropical, and one is regional. The regional species is the Magnificent Frigatebird (Fregata magnificens), which predominates in the Americas and is the only species that is ordinarily found along continental coastlines, so it is observed far more often than the others. There is some uncertainty about the taxonomic status of one or two isolated populations, especially the Atlantic population of Lesser Frigatebird (Fregata ariel), so it is possible that additional species may eventually be recognized.
Lesser Frigatebird (Fregata ariel)
“Lesser Frigatebird” (F. a. ariel)
“Trindade Frigatebird” (F. a. trinitatis)
Ascension Frigatebird (Fregata aquila)
Magnificent Frigatebird (Fregata magnificens)
Great Frigatebird (Fregata minor)
Christmas Frigatebird (Fregata andrewsi)
References
Boyd, J.H., 2019. Taxonomy in Flux: Mirandornithes & Ardeae II. http://jboyd.net/Taxo/List8a.html#suliformes. (Posted August 6, 2019; Accessed August 6, 2020.)
Harrison, P. 1983. Seabirds: An Identification Guide. Houghton Mifflin, Boston.
Howell, S.N.G., and K. Zufelt. 2019. Oceanic Birds of the World. Princeton University Press.
Olson, S.L. 2017. Species rank for the critically endangered Atlantic Lesser Frigatebird (Fregata trinitatis). Wilson Journal of Ornithology 129:661-675.
Roberson, D. 2008. Bird Families of the World: Frigatebirds, Fregatidae, http://creagrus.home.montereybay.com/frigatebirds.html. (Posted February 16, 2008. Accessed August 6, 2020.)