Andean gull

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The Andean gull (Chroicocephalus serranus) is a large gull that lives in the Andes of South America, from southwestern Colombia down to Chile and Argentina.

Description
- It is about 42–48 cm long and weighs around 480 g.
- Adults in breeding plumage wear a glossy black hood, a white crescent behind the eye, a mostly white body, a gray back, and a white tail. Their wings are gray on top with a white–black–white–black pattern on the primaries. The underwing is pale gray with a black outer half and large white “mirrors” on the outer primaries. The bill and legs are dark brown with a reddish tint, and the iris is brown.
- Non-breeding adults have a white head and blackish legs.
- It takes about two years to reach full adult plumage.

Habitat and range
- The Andean gull stays in the Andes year-round, from far southwestern Colombia through Peru, western Bolivia, and into eastern Chile and western Argentina, up to about northern Chile’s Aysén Region.
- Many birds winter along the coast, from central Peru into northern Chile. It has been recorded as a rare vagrant in Amazonian Peru and southern Argentina.

Breeding
- Breeding mainly occurs in July and August, sometimes in small colonies but often solitary.
- Nests are built along riverbanks or on islands in rivers and lakes, in puna and páramo zones at high elevations (roughly 3,000–5,300 m, sometimes down to 1,200 m in the southern range).
- Clutch size is usually two or three eggs, but one or four eggs can occur. Details about incubation and parental care are not well known.

Diet
- In the mountains, they eat earthworms, insects, amphibians, small fish, and occasionally eggs or chicks of waterbirds.
- In winter, they also scavenge at ski resorts.
- Along the coast, they eat offal, fish, and marine invertebrates.
- They move by walking, swimming, and flying to find food.

Vocalizations
- They make agitated, sometimes tremulous “yeeer” calls and a hoarse “raggh-aggh-keeaagh” plus other low raspy sounds.

Conservation
- The IUCN lists the Andean gull as Least Concern. It has a large range, but the exact population size is unknown. No immediate threats have been identified, though breeding areas in remote high-altitude lakes may face increasing agricultural pressure and disturbance.