Andean Gull Chroicocephalus serranus Scientific name definitions

The Andean Gull is a somewhat non-classic Chroicocephalus gull. In appearance the dark hood, pale back and pattern of black and white on the primaries is typical of this genus. However, ecologically it is odd in that it chooses to breed strictly in montane settings. These include very high elevation wetlands in the Altiplano, over 4000m in elevation. Farther south it may breed much lower down, less than 2000m, but still in ecologically montane habitats. In some regions the Andean Gull is resident, such as in the Altiplano. On the other hand in regions where the highlands become less hospitable in the winter, the Andean Gull descends to lower elevations. Interestingly, they are fond of the coast when they descend and are less likely to be seen in inland bodies of water. Flocks of non-breeding Andean Gulls are common in winter in southern Peru and northern Chile, it is a mystery as to whether they are from adjacent highland areas (where many Andean Gulls are resident), or if these coastal congregations involve birds that breed much farther south. The Andean Gull is also unusual for a Chroicocephalus in that it is a rather large species, much bulkier and heavier than average member of this genus. Even though it is the size of many gulls that are considered “three-year” gulls in their maturation progression, the Andean Gull has the classic one cycle of immaturity and then the adult plumage of a “two-year” gull.

44–48 cm; 478 g. Two-year gull. Breeding adult has glossy black hood , with white rear eye-crescents ; neck white; back and upperwing grey; unique wing pattern , with broad dark band across middle of black-tipped white primaries, creating white-black-white-black pattern; from below, distal half of wing mainly blackish, with large white mirrors on three outermost primaries; underparts white, sometimes suffused pink; bill  , legs and feet blackish brown, tinged reddish; iris brown. Non-breeding adult  lacks black head  and has blackish legs, similar to smaller L. maculipennis. First-year bird  more likely to be confused with L. cirrocephalus; has complex black-and-white pattern on upper primaries  and secondaries, partially dark head , and black subterminal tail-band.

Andean lakes from N Ecuador, W Bolivia and NW Argentina (Tucumán) to C Chile (Ñuble, rarely to Aisén). Individuals and small flocks also reported from SW Colombia at Laguna La Cocha (1 Strewe, R. (2000). New distributional sightings of 28 species of birds from Dpto. Nariño, SW Colombia. Bulletin of the British Ornithologists’ Club 120(3):189–195. Close ). In winter extends to Pacific coast, mainly from C Peru to N Chile.

During the breeding season frequents lakes, bogs with small ponds, marshes and fields; breeds on riverbanks, or on small islets in altiplano lakes, usually at altitudes of 4000–5300 m, occasionally lower. Winters on adjacent Pacific coast.

Many birds remain on altiplano lakes and marshes throughout year, but most descend to congregate at river mouths on Pacific coast; flocks common in winter in S Peru and N Chile. Individuals and small flocks also reported in SW Colombia at Laguna La Cocha in Nov and Jan (1 Strewe, R. (2000). New distributional sightings of 28 species of birds from Dpto. Nariño, SW Colombia. Bulletin of the British Ornithologists’ Club 120(3):189–195. Close ).Occasionally reaches Atlantic coastal plain, where perhaps otherwise overlooked. Two individuals in breeding plumage recorded in Dec 2009 in S Argentina (2 Roesler, I., Imberti, S., Casañas, H.E., Hernández, P.M., Klavins, J.M. and Pagano, L.G. (2014). Noteworthy records and natural history comments on rare and threatened bird species from Santa Cruz province, Patagonia, Argentina. Rev. Bras. Orn. 22(2): 189–200. Close ).

Breeders feed along rivers and on grasslands. Diet includes earthworms, insects , amphibians and small fish, and sometimes eggs and chicks of various waterbirds. Outside breeding season, takes offal, marine invertebrates and fish.

Gives agitated, sometimes tremulous “yeeer” calls. Also a hoarse “raggh-aggh-keeaagh” and other low raspy notes (3 Fjeldså, J., and N. Krabbe (1990). Birds of the High Andes: A Manual to the Birds of the Temperate Zone of the Andes and Patagonia, South America. Zoological Museum, University of Copenhagen and Apollo Books, Copenhagen and Svendborg, Denmark. Close ).

Nests mainly Jul–Aug, but variable, depending on climate. Breeding biology largely unknown. Usually in small colonies, which are remarkably silent; sometimes solitary. Birds leave when intruders approach. Nest among tall grasses and rocks on vegetated islands, or builds floating nest anchored to emergent vegetation, up to 1 m above water. Nests 1–3 m apart (mean 1·3 m), usually at base of rock or vegetation. Usually 2–3 eggs (1–4); eggshell has reduced pores and lower water-vapour conductance than those of gulls breeding at sea-level, but water loss is greater because of increased gaseous diffusion and lower barometric pressure at high altitude; reported to leave eggs unattended for long periods while feeding, but this seems unlikely. Attains adult plumage by two years old, but age of first breeding not known.

Not globally threatened (Least Concern). Total population unknown but estimated at 150,000 individuals. The species is probably vulnerable, with no large populations. Centre of abundance in S Peru and N Chile. Most breeding areas are in remote high-altitude lakes but many are increasingly subject to agricultural pressure and human disturbance.