Bridled tern

Bridled tern
	Adult on Lady Elliot Island, Australia
Conservation status
	; Least Concern (IUCN 3.1)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Charadriiformes
Family:	Laridae
Genus:	Onychoprion
Species:	O. anaethetus
Binomial name
	Onychoprion anaethetus; (Scopoli, 1786)
Synonyms
	Sterna anaethetus Scopoli, 1786

The bridled tern (Onychoprion anaethetus)^[2]^[3]^[4] is a seabird of the family Laridae. It is a bird of the tropical oceans. The scientific name is from Ancient Greek. The genus comes from onux meaning "claw" or "nail", and prion, meaning "saw". The specific anaethetus means "senseless, stupid".^[5]

Description

This is a medium-sized tern, at 30–32 cm in length and with a 77–81 cm wingspan similar to the common tern in size, but more heavily built. The wings and deeply forked tail are long, and it has dark grey upperparts and white underparts. The forehead and eyebrows are white, as is a striking collar on the hindneck. It has black legs and bill. Juvenile bridled terns are scaly grey above and pale below.

This species is unlikely to be confused with any tern apart from the similarly dark-backed sooty tern and the spectacled tern from the Tropical Pacific. It is paler-backed than that sooty, (but not as pale as the grey-backed) and has a narrower white forehead and a pale neck collar.

Distribution and movements

This bird is migratory and dispersive, wintering more widely through the tropical oceans. It has markedly marine habits compared to most terns. The Atlantic subspecies melanopterus breeds in Mexico, the Caribbean and west Africa; other races occur around the Arabian Peninsula and in Southeast Asia and Australasia, but the exact number of valid subspecies is disputed. It is a rare vagrant to western Europe. These are the four subspecies listed by the IOC:

O. a. melanopterus – (Swainson, 1837): Caribbean and West Africa.
O. a. antarcticus – (Lesson, 1831): Red Sea, Persian Gulf and western Indian Ocean.
O. a. anaethetus – (Scopoli, 1786): eastern Indian, and Pacific Oceans.
O. a. nelsoni – (Ridgway, 1919): west coast of Mexico and Central America.

Breeding

This species breeds in colonies on rocky islands. It nests in a ground scrape or hole and lays one egg. It feeds by plunge-diving for fish in marine environments, but will also pick from the surface like the black tern and the gull-billed tern. It usually dives directly, and not from the "stepped-hover" favoured by the Arctic tern. The offering of fish by the male to the female is part of the courtship display.

Lady Elliot Island, Qld, Australia

Various views and plumages

In non-breeding plumage
Bridled tern, at rookery
Juvenile on Lady Elliot Island, Queensland, Australia
In flight Lady Elliot Island, Queensland, Australia
Juvenile bathing at Perth Zoo
Juvenile or adult with non-breeding plumage taking off from a sea debris perch during Pelagic expedition off coast of Malpe
O. a. antarcticus after dive (composite)
ID composite
With egg in nest under boardwalk steps on Penguin Island, Western Australia