Inca tern

The  Inca tern (Larosterna inca) is a near-threatened species of tern in the subfamily Sterninae of the family Laridae (the gulls, terns, and skimmers). It is found along the Pacific coasts of Chile, Ecuador and Perú, and has appeared as a vagrant in Central America and Hawaii.

Taxonomy and systematics
The Inca tern is the sole member of its monotypic genus, Larosterna, and has no recognized subspecies.



Description
The Inca tern is roughly 39 to 42 cm long and weighs between 180 to 210 g. Its plumage is uniquely colorful, among terns; adults have a mostly dark, slate-gray body, with a paler throat and underwing coverts. A white stripe extends back from the base of the bill and fans-out as long, satiny feathers along the side of the neck. The trailing edge of their wing, and the edges of the four outer primaries, are white. Their tail is black and moderately forked. Their iris is brown, with legs and feet that are dark red. Their bill is dark red with bare yellow skin at the base. Chicks are, upon hatching, a purplish-brown, progressing through brownish-gray before developing mature plumage. The chicks' bills and legs are dark and horn-colored, and gradually attain the red of adults'.

Distribution and habitat
The Inca tern is an inhabitant of the Humboldt Current region. It breeds from Lobos de Tierra, in northern Perú, south to the Aconcagua River, near Valparaíso, Chile. Some disperse north into Ecuador after breeding. It is a casual visitor to Panamá and Costa Rica, and has also been recorded as a vagrant in Guatemala and Hawaii. The Hawaiian documented birds, in particular, remained from March through November on the Hawaiian archipelago.

The South American Classification Committee of the American Ornithological Society treats the Inca tern's presence in Colombia as "hypothetical", due to a number of unverified or undocumented sightings. On the biodiversity database iNaturalist, one 'research-grade' sighting (with photo) has been documented from the coast of Buenaventura, Colombia's Isla Cascajal, dated July 2023.

The Inca tern nests on sea cliffs and guano islands, as well as manmade structures (such as ledges under piers) and abandoned barges. It will gather with other sea and shorebirds on sandy beaches.

Movement
The Inca tern is essentially non-migratory, although some disperse northwards after breeding. Some rogue individuals have flown great distances.

Feeding
The Inca tern feeds primarily on small fish, such as anchoveta (Engraulis ringens), and also consumes planktonic crustaceans and offal or carrion in its diet. Large flocks congregate around fishing boats and will also follow the feeding patterns of cormorants, sea lions, and whales and dolphins. Feeding flocks can number over 5,000 birds. The Inca tern catches its prey mainly by plunge-diving, but also picks items from the surface while flying or floating on the water.



Breeding
The Inca tern's breeding does not appear to be concentrated in any season. Eggs have been found between April and July and between October and December, and other evidence of breeding has been noted in August. It nests in a variety of sites including fissures and caves in rock cliffs, among rocks and boulders on island slopes, in abandoned petrel and penguin burrows, and on and under human structures. The clutch size is usually two eggs though sometimes one. Both sexes incubate the clutch and provision the young. The incubation period is not known; fledging occurs about four weeks after hatch and the young are fully dependent on the adults for at least a month after fledging.

Vocalization
The Inca tern is most vocal at its nesting colonies. Its calls include "raucous cackling notes" and "mewing"; the latter call has been likened to that of a kitten.

Status
The IUCN has assessed the Inca tern as Near Threatened. It has a somewhat restricted range; its population size is not known and is believed to be decreasing. "Reproductive success is dramatically reduced during El Niño events". Human harvesting of its primary prey is a probable threat as is climate change. One estimate placed its population at about 150,000 in 2011.