About Theristicus caerulescens (Vieillot, 1817)
The plumbeous ibis (Theristicus caerulescens), formerly also called the blue ibis, is a large, distinctive ibis species that is endemic to parts of central South America. This species has a relatively narrow range extending through parts of central South America. It occurs in south-western Brazil, particularly southern Mato Grosso and Rio Grande do Sul; Paraguay, particularly the Chaco and the Paraguayan section of the Paraná Basin; Uruguay; north-eastern Argentina; and northern and eastern Bolivia. The northern Bolivian population is geographically isolated from the larger continuous population that covers the rest of this ibis's range. The westernmost part of its range reaches the Andean foothills in central Bolivia and Tucuman. In Argentina, individuals have occasionally been sighted as far south as the Córdoba and Buenos Aires provinces, but the species is non-native in these regions. Although the species is relatively common overall, it is patchily distributed across its global range, being relatively abundant in some areas and less common in others. For example, while it is endemic to Rio Grande do Sul, it is actually uncommon there, but occurs frequently in the northern Lagoa dos Patos. It is relatively common in the Paraguayan Chaco, especially the northern Chaco where large numbers of individuals live across expanses of freshwater; this species is considered emblematic of the wetland bird community of this region. In contrast, it has rarely been recorded in the pampas of northern Argentina, the southernmost part of its distribution. Throughout the 1990s, an occasional small number of individuals were sighted during surveys at the Laguna Melincue Ramsar Site in southern Santa Fe Province. Its habitat mostly consists of lowland grassy wetlands of the Pantanal and the Chaco. It forages in marshes, swamps, lagoons, shallow lakes, flooded pastures, ponds and other moist ground, and perches on tree branches near or above water to roost. It has also been sighted in upland marshes, typically up to 600m in elevation, at small remnant pools in desiccated lagoons, and on dry grasslands. This ibis also commonly occurs near human settlements and other manmade features, including dams and seasonally flooded rice fields. It is also a relatively common sight along the Transpantaneira Highway in the Pantanal of Mato Grosso. Finally, it has been recorded close to the east Brazilian coast in wet areas in the Lagoa do Peixe National Park on the peninsula that separates Lagoa dos Patos from the Atlantic, as documented by Pereira & Poerschke in 2009, but the species probably avoids saline and brackish waters. Individuals are usually sedentary and can stay in one area year-round. However, they have been reported to migrate over local scales. Circumstantial evidence from the unexpected presence of individuals at Incachaca Lake in the Chapare Province of Bolivia suggests that this species may migrate between the geographically separated northern Bolivian population and other South American populations, and may use Incachaca as a resting spot along the route. Since no subspecies have been recognized for this species, the global population is likely kept genetically homogenous by short migrations of individuals between the two geographically separated subpopulations. Still, it is not known whether this species has regular migration patterns. The discovery of the species at Lake Incachaca was the first recorded occurrence of the species in the cloud forest ecoregion, and also set a new altitudinal record for the species. Unlike other ibis species, the plumbeous ibis does not form large flocks of its own species. It is most often seen alone or in pairs, and groups of up to six individuals are seen more rarely. Larger groups usually consist of a mated pair accompanied by their fledged juveniles.
