Fregata minore

Identificazione

The lesser frigatebird is the smallest species of frigatebird and measures 66–81 cm (26–32 in) in length with a wingspan of 155–193 cm (61–76 in) and long forked tails. Male birds weight 625–875 g (1.378–1.929 lb). Female birds are heavier and weight 760–955 grams (1.676–2.105 lb). Like all frigatebirds the male has a large red sac on the front of the throat which is inflated during courtship. Courtship display also involves a variety of calls, bill rattling and spreading of the wings. The male is mostly all black save for a white patch on the flank which extends on to the underwing as a spur. Males also have a pale bar on the upper wing. Females have a black head and neck with a white collar and breast as well as a spur extending on to the underwing. The female also has a narrow red ring around the eye. 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.<p>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. They have a very light skeleton and long narrow wings and are masters of the air. Their name probably derives from the fact that they harass other sea birds such as boobies and tropicbirds as they return to their nests from feeding, forcing them to disgorge their catch, which is then swooped upon and caught by the frigate birds before it reaches the water below. 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.

Tassonomia

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. The lesser frigatebird is one of five closely related species of the genus Fregata. The other four are: the great frigatebird (Fregata minor), the Christmas frigatebird (Frigata andrewsi), the magnificent frigatebird (Fregata magnificens) and the Ascension frigatebird (Fregata aquila). The genus is the only member of the family Fregatidae.<p>Three subspecies are recognised:<p>Some ornithologists have questioned the validity of these subspecies as they appeared to differ only in their size. Few museum specimens of the isolated Atlantic F. a. trinitatis exists, making comparisons difficult, but a comprehensive study published in 2017 found that it differed in both color of plumage and skeletal details, leading to the recommendation of treating it as a separate species (Fregata trinitatis).

Nome scientifico

Fregata ariel

Autorità

(Gray, GR, 1845)

Ordine

Suliformi

Famiglia

Fregatidi

Genere

Fregata

Areale e habitat

The lesser frigatebird is said to be the most common and widespread frigatebird in Australian seas (Lindsey, 1986). It is common in tropical seas, breeding on remote islands, including Christmas Island in the Indian Ocean in recent years. These birds are most likely to be seen from the mainland prior to the onset of a tropical cyclone, and once this abates they disappear again.

Areale riproduttivo

TrO : widespread, tropical Indian and Pacific ocean is., also nw South Atlantic

Areale non riproduttivo

to waters off se Africa, sw India and Sri Lanka, throughout Indonesian Arch. and Philippines to Taiwan, New Guinea waters, n Australia and Melanesia

Migrazione

Resident species

Conservazione

Tendenza della popolazione

declining