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.