The lesser frigatebird is a lightly built seabird with brownish-black plumage, long narrow wings and a deeply forked tail.

The lesser frigatebird was first described as Atagen ariel by the English zoologist George Gray in 1845 from a specimen collected on Raine Island, Queensland, Australia.

Juveniles and immature birds are more difficult to differentiate but the presence of the spurs of white in the armpits is a helpful distinguishing sign.

Frigate birds are built for flying; they rarely swim and cannot walk but can manage to climb around the trees and bushes in which they nest.

This practice seems to be more common among female frigate birds, but probably only accounts for a fairly small proportion of the diet, which mainly consists of squid and flying fish scooped up from the surface of the sea.

[11] Because of the large overall population and extended range the species is classified by the International Union for Conservation of Nature as being of Least Concern.

[1] In the South Atlantic, lesser frigatebirds (subspecies F. a. trinitatis) once bred on Fernando de Noronha, Saint Helena and Trindade.

The Fernando de Noronha and Saint Helena populations disappeared in ancient times and are only known from subfossil remains, estimated to be a few hundred years old.

[12] The main island of Trindade was once covered in forest but after this was destroyed, overgrazing by the introduced goats prevented any recovery.

In 1975–1976 the ornithologist Storrs Olson visited the island and reported seeing a small colony of 15 nests on a rocky islet just off the southern coast.

[10] Combined, these sightings suggest that the remaining South Atlantic population is tiny, possibly numbering less than 20 breeding pairs.