Plumbeous Ibis

Identification

This large ibis measures 71–77 cm in length, with a wing length of 397-450mm in males and 360-406mm in females. The culmen length is 145-167mm in males, and 126-147mm in females. The sexes are similar in appearance, but the female is slightly smaller. The plumbeous ibis is easily recognisable through a distinctive shaggy crest comprising long grey plumes that extend from the back of head 10 cm down the nape. A prominent, narrow, white feathered band also extends around the forehead, which has earned this species the German common name Stirnbandibis (headband ibis). Overall, it is readily distinguishable in the field from other ibises by its solid colouration and thick neck. The plumbeous ibis is the most morphologically similar to the sympatric buff-necked ibis Theresticus caudatus, but differs in colouration and neck structure.<p>The adult plumage is usually grey; but can be bluish grey, greenish grey or brownish grey. The dorsal feathers are mottled greyish-brown, so that the plumage appears lighter below than above. The flight and tail feathers are dark brown or black, superimposed with a glossy greenish bronze. It has also been reported as having various other subtle tinges on the body depending on the light. When the bird is seen in the correct light, Hudson has described the plumage as appearing silvery grey, the top of the head as dark brown with a greenish tinge, the primary feathers as dark blue, the tail as dark green, and the feathers of the throat and neck as light brown with an occasional pinkish tinge. <p>The black, downward-curved bill is serrated between the mandibles. The bare skin of the lores and throat is black or dark grey. The legs are a pinkish orange, darkening in the breeding season in preparation for courtship. The iris is deep orange, but has been noted to be slightly paler around the pupil. In some individuals, the iris has also been reported to be brownish yellow.<p>The chicks have light grey downy plumage that lacks the more sophisticated tinges in adults. Fledged young are also distinguishable from adults by a dark iris, grey legs, a less developed nuchal crest, a more extensive white band on the forehead and red bare skin patches. The white band on the forehead begins to develop in the young after 18 days of age and up close appears a brighter white than that of adults.<p>Through its powerful musculature, this ibis is sturdy and direct in flight; stretching out its neck and wings and steadily beating its wings with intermittent gliding.<p>The loud vocalisations uttered by this species are diverse. The basic call is a high-pitched, rapid pi-pi-pi-pi which has a somewhat metallic timbre and can be uttered when the bird stands on the ground during daytime. This call has been said to resemble the sound of a banjo with brass strings so big that it could be heard a mile and a half away.<p>This ibis also makes a slow but energetic trumpeting flight call that has been transcribed as kree kreee kree or k k kuh kuh KEE KEE KEE KEE KEE KEE KEE keh kuh kuh. While making flight calls, it glides through the air with motionless downward curved wings. It also utters a nasal, high-pitched, rapid series of cackles when perched on branches or at the nest site transcribed as tututututu; sometimes interspersed with elements of ti-ti and often in duet between mates large distances apart. Another contact call is made between foraging mates and has been transcribed as a cackling kuk-kuk…kuk-kuk…kuk kuk. Overall, the broad range of loud distinctive calls of this species indicates the importance of long-range communication between individuals, especially mates.

Taxonomy

The plumbeous ibis has historically undergone frequent reclassification and been placed in various genera such as Molydophanes, Geronticus, Theresticus and Harpiprion. It has also been referred to as Ibis caerulescens and Theresticus (Harpiprion) caerulescens. Nevertheless, this ibis has traditionally been assigned to the monotypic genus Harpiprion, carrying the binomial name Harpiprion caerulescens; on the basis that this species was previously believed to have no close relatives. However, phylogenetic analyses based on both nuclear and mitochondrial DNA markers have suggested that the plumbeous ibis is closely related to other ibis species in the genus Theresticus such as the buff-necked ibis; given the markedly low genetic distances between the plumbeous ibis and other Theresticus species. Hence, the current placement of the plumbeous ibis in the genus Theresticus appears justified.

Scientific name

Theristicus caerulescens

Authority

(Vieillot, 1817)

Order

Pelecaniformes

Family

Threskiornithidae

Genus

Theristicus

Range and habitat

The plumbeous ibis has a relatively narrow range that extends through parts of central South America. It occurs in south-western Brazil, especially in southern Mato Grosso and Rio Grande do Sul; Paraguay, especially in the Chaco and in the Paraguayan section of the Parana Basin; Uruguay; north-eastern Argentina and northern and eastern Bolivia. The northern Bolivian population is geographically isolated from the larger continuous population spanning the remaining part of this ibis's range. The westernmost part of its range extends into the Andean foothills in central Bolivia and Tucuman. In Argentina, it has been occasionally sighted as far south as the Cordoba and Buenos Aires provinces; but is non-native in these regions.<p>Although this species appears to be relatively common, it is patchily distributed throughout its global range; being relatively abundant in some regions but less so in others. For example, it is endemic but actually uncommon in Rio Grande do Sul, but frequently occurs in the northern Lagoa dos Patos. It is relatively common in the Chaco of Paraguay, especially in the northern Chaco where large numbers of individuals occur throughout the expanses of freshwater, so that this species is considered emblematic of the wetland avifauna of this region. Conversely, it has rarely been recorded in the pampas of northern Argentina in the southernmost part of its distribution; with an occasional handful of individuals at a time having been sighted during surveys throughout the 1990s in the Laguna Melincue Ramsar Site in the southern Santa Fe Province.<p>Its habitat largely comprises the lowland grassy wetlands of the Pantanal and the Chaco. It is found here foraging at marshes, swamps, lagoons, shallow lakes, flooded pastures, ponds and other moist ground; but also perches in tree branches near or above the water to roost. It has also been sighted in upland marshes, usually up to 600m in elevation; and at small remnant pools in desiccated lagoons and on dry grasslands. Further, this ibis commonly occurs near human habitation 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 separating Lagoa dos Patos from the Atlantic (Pereira &amp; Poerschke, 2009); but probably avoids the saline and brackish waters.<p>Individuals are usually sedentary and can remain in a specific area all year round. They have however been reported to migrate on a local scale. Circumstantial evidence from the novel presence of individuals at Incachaca Lake in the Chapare Province of Bolivia suggests that this species may migrate between the geographically separated northern Bolivian and other South American populations, and may use Incachaca as a resting place en route. Since no subspecies have been noted for this species, the world population is probably kept genetically homogenous by short migrations of individuals between the two geographically separated subpopulations. However, it remains unknown whether this species has regular migration patterns. Incidentally, the species’ discovery at Lake Incachaca was its first recorded occurrence in the cloud forest ecoregion and was also a new altitudinal record.<p>Unlike other ibis species, the plumbeous ibis does not form large intraspecific flocks. It is most often seen singly or in pairs, but is also more rarely seen in groups of up to six individuals. The larger groups appear to consist of two mates accompanied by their fledged juveniles.

Migration

Resident species

Behavior

Migration pattern: Resident species.

Conservation

Population trend: stable.

Population trend

stable