Andean Gull

The Andean gull (Chroicocephalus serranus) is a striking bird, one of the larger members of its genus, measuring 42 to 48 cm in length and weighing approximately 480 grams. Both sexes are similar in appearance, with adults donning a glossy black hood and a white crescent behind the eye during the breeding season. Their plumage is predominantly white with a gray back, and some may exhibit a subtle pink flush on the underparts. The tail is white, and the wings are gray with a distinctive white-black pattern on the primaries. Their bill, legs, and feet are a blackish brown with a reddish hue, and their eyes are brown. In non-breeding plumage, adults have a white head and blackish legs. Juveniles take two years to reach full adult plumage, featuring mottled black on the head and a complex black and white pattern on the wings, including a black band near the tail's end.

Identification Tips

When identifying the Andean gull, look for the black hood and white crescent behind the eye in breeding adults. The wing pattern is also a key feature, with the upper side showing a gray base and the white-black alternation on the primaries. The large white "mirrors" on the outermost primaries are visible on the underside of the wing. The reddish tinge to the blackish bill, legs, and feet can also aid in identification.

Habitat

The Andean gull is typically found in the puna and páramo zones of the Altiplano during the breeding season, frequenting lakes, bogs, marshes, and fields. It inhabits elevations mostly ranging from 3,000 to 5,300 meters but can be found as low as 1,200 meters in the southern part of its range.

Distribution

This species resides year-round in the Andes, from southwestern Colombia through central Ecuador and Peru, western Bolivia, eastern Chile, and western Argentina, extending to the latitude of northern Chile's Aysén Region. In winter, many individuals migrate to coastal areas from central Peru to northern Chile.

Behaviour

The Andean gull is versatile in its feeding habits, consuming earthworms, insects, amphibians, small fish, and occasionally the eggs and chicks of other waterbirds in the mountains. Along the coast, it scavenges and feeds on offal, fish, and marine invertebrates. It is known to walk, swim, and fly in pursuit of food.

Song & Calls

The vocal repertoire of the Andean gull includes agitated, sometimes tremulous "yeeer" calls, a hoarse "raggh-aggh-keeaagh," and other low raspy notes.

Breeding

Breeding primarily occurs in July and August. The Andean gull may breed solitarily or in small colonies, with nests situated along riverbanks and on islands within rivers and lakes. Clutch sizes typically range from one to four eggs, with two or three being most common. Specific details on incubation periods, fledging times, and parental care are not well documented.

Similar Species

While there are no specific similar species mentioned, when identifying the Andean gull, it is important to note the unique features that distinguish it from other gulls, such as its black hood and the specific wing patterns.

Diet and Feeding

The Andean gull's diet is diverse, including earthworms, insects, amphibians, small fish, and sometimes the eggs and chicks of other waterbirds in the mountains. Along the coast, it feeds on offal, fish, and marine invertebrates, and is known to scavenge at ski resorts during winter.

Conservation status

The IUCN has classified the Andean gull as Least Concern. Although it has a large range, the population size and trend are not well known. There are no immediate threats identified, but the species is considered potentially vulnerable due to human disturbance and agricultural pressure on its breeding habitats.