Clytoctantes

The genus Clytoctantes belongs to the family Thamnophilidae, a diverse and extensive clade of New World suboscine passerines often called antbirds. Thamnophilidae contains approximately 200 species spread across 63 genera, most of which inhabit tropical forest undergrowth and track swarms of army-ant to dine on insects caught there.^[9] Within this family, Clytoctantes is grouped alongside the genus Neoctantes in the tribe Microrhopiini (subfamily Thamnophilinae), a lineage characterized by the presence of robust bills adapted for probing into woody stems and bamboo culms.^[9]

Daniel Giraud Elliot erected the genus Clytoctantes in 1870, and the recurve-billed bushbird, Clytoctantes alixii, was designated as the type species.^[10] Clytoctantes alixii retains the original binomial and authority and is readily recognized by its unique upward-curved bill. The second species, Clytoctantes atrogularis, was described many years later by Lanyon, Stotz, and Willard in 1991, based on a holotype from the interfluvial forests of Rondônia, Brazil.^[11]

Clytoctantes is a genus in the antbird family (Thamnophilidae) found in South America. Males of this genus are predominantly black, while females typically have reddish-brown or chestnut-colored plumage.^[2] The genus includes two recognized species: the recurve-billed bushbird (Clytoctantes alixii) and the Rondônia bushbird (Clytoctantes atrogularis).^[3]

These birds are medium-sized and sexually dimorphic, with a distinctive, robust, laterally compressed black bill.^[2] The lower mandible is sharply upturned, giving the bill a unique shape.^[2] The strong resemblance in bill structure and size between Clytoctantes alixii and Clytoctantes atrogularis suggests a shared evolutionary lineage.^[2] Their chestnut-colored plumage further supports their classification within the Clytoctantes genus.^[2] The holotype of Clytoctantes atrogularis is generally larger than the examined female specimens of Clytoctantes alixii, with a notably longer tail.^[2] While Clytoctantes atrogularis has an entirely black bill, preserved specimens of Clytoctantes alixii show pale markings on the bill.^[2]

Both species were once thought to be at risk of extinction, but they were rediscovered in 2004.^[6] Subsequent monitoring efforts took place between 2014 and 2017, confirming their continued existence.^[6]

• Recurve-billed bushbird (Clytoctantes alixii)
• Rondônia bushbird (Clytoctantes atrogularis)

The name "bushbird" is shared with the rather similar, but smaller-billed black bushbird from the monotypic genus Neoctantes.

Clytoctantes alixii is a medium-sized bird with predominantly chestnut-colored plumage.^[2] Its most distinctive feature is its uniquely curved bill, which bends upward.^[2] While its bill is generally black, preserved specimens show pale markings.^[2] Males of Clytoctantes alixii have a striking black throat and breast, which contrast with their dark grey abdomen and back.^[12] Their forehead and lores are also black, creating a sharp distinction from the darker brown crown and back.^[12] In females, the underparts are a uniform chestnut, and unlike some related species, they do not have a black patch on the throat or breast.^[2] A key identifying feature is that both male and female Clytoctantes alixii have spotted wing coverts.^[2] In females, these spots are pale buff, while in males, they are black or black with white centers.^[2] The lower back and tail coverts in females are brown, and the rectrices are a more muted brownish grey.^[2] The contrast in plumage colors is particularly pronounced in males, where the chestnut underparts stand out against the darker upper body.^[12]

The female Clytoctantes atrogularis has a predominantly chestnut-colored body, with a distinctive black patch covering the chin, throat, and upper breast.^[2] Its tail and tail coverts are dark grey, setting it apart from the female Clytoctantes alixii, which lacks this black "bib" and has marked wing coverts.^[2] The head and upper back are a deep chestnut, gradually fading to brown on the lower back.^[2] A small, hidden white patch is present between the shoulders.^[2] The tail feathers are nearly black, while the underparts transition from chestnut on the lower breast and abdomen to grey on the vent and under-tail coverts.^[2] The wings are dark chestnut with unmarked upper wing coverts, and the flight feathers are dark brown with lighter brown leading edges.^[2] The bill is large, laterally compressed, and features a distinctive upturned lower mandible.^[2] In life, the bill, legs, and feet are black, while the eyes are dark brown.^[2] The male has an overall dark, blackish-grey plumage, with a slightly darker throat and a concealed white patch on the back.^[12] A sub-adult individual has some brownish feathers on the head and wings.^[12] The measurement of the holotype shows that its flattened wing measures 79.0 mm and the tail is 64.5 mm.^[2]

Clytoctantes alixii has a highly restricted range and is known from only a few locations in northwestern Venezuela and northern Colombia.^[4] In Venezuela, it has been recorded in the Sierra de Perijá, an isolated mountain range along the border with Colombia.^[4] In Colombia, it has been documented in the foothills of the Magdalena Valley, particularly in Santander and Cesar, as well as in the Serranía de San Lucas in Bolívar.^[7] Additionally, it has been observed in various foothill locations north of the Andes, including Antioquia, Córdoba, and Caldas.^[4] The species was first recorded in 1914 in the Cordillera Central of the Colombian Andes, specifically in northern Antioquia.^[7] However, after a sighting in the Serranía de Abibe in 1965, Clytoctantes alixii went unreported for decades, leading to concerns that it might be extinct.^[7] It was not until 2004 that the species was rediscovered in Venezuela.^[7] A year later, in 2005, another population was found in Norte de Santander, Colombia, at elevations between 1,600 and 1,750 meters—considerably higher than previous records.^[4] The southernmost known sighting comes from eastern Caldas.^[4]

Clytoctantes atrogularis is a species found exclusively in the Amazon region of Brazil, where it inhabits the forests between the Madeira and Tapajós rivers.^[5] Its known range spans the states of Amazonas, Mato Grosso, and Rondônia, with natural boundaries formed by the Madeira River to the west and the Sucunduri and Tapajós rivers to the east.^[5] Though initially known from only a few locations, subsequent surveys have expanded the number of recorded sites where Clytoctantes atrogularis has been observed. In Mato Grosso, it has been documented in Alta Floresta and within Igarapés do Juruena State Park.^[8] In Amazonas, sightings have occurred along the Rio Sucunduri and near Pousada Rio Roosevelt.^[8] In Rondônia, it has been recorded in the Jaru Biological Reserve.^[8] These findings suggest that Clytoctantes atrogularis may have a wider distribution within this interfluvial region than previously thought.^[8]

Clytoctantes alixii inhabits lowland and foothill forests at elevations ranging from 185 to 1,750 meters.^[4] It prefers areas with dense undergrowth, including thickets, forest edges, young secondary growth, and regenerating forests.^[4] In Venezuela, the species has been observed in the thick understory of secondary habitats, such as old swidden plots, and appears to favor steep slopes with high water runoff in decaying woodland.^[4] In Colombia, its habitat varies, with sightings in mature secondary forests with a significant bamboo presence, as well as in overgrown, rocky gullies without bamboo.^[7] In Antioquia, Clytoctantes alixii has been found at lower elevations, between 300 and 800 meters, in secondary forests with a dense understory.^[4] The species is believed to breed between April and May in the western part of its range, while in Caldas, the reproductive period may begin as early as January.^[4] Its feeding behavior primarily involves pecking open hollow stems and branches to extract insects, suggesting an adaptation to foraging in decaying vegetation.^[4] The species has been observed foraging in areas with vine tangles and thickets, as well as on dead stems and branches of fallen trees.^[7]

Clytoctantes atrogularis lives in the understory of terra firme forests, which are forests that do not flood.^[8] It prefers areas with dense vine tangles, understory palms, and small openings created by fallen trees.^[5] The species has also been found near small streams and in patches of Guadua bamboo.^[5] Although it is mainly found in undisturbed forests, it has occasionally been observed in areas that have been selectively logged or partially cleared for agriculture.^[5] In some parts of its range, Clytoctantes atrogularis has been recorded in campinarana forests, a unique type of vegetation in the Brazilian Amazon that grows on white-sand soils.^[8] These forests have a low, dense canopy with many small trees but lack large, towering emergent trees and climbing plants like lianas.^[8] Clytoctantes atrogularis is insectivorous, primarily eating ants.^[5] It looks for food by moving through dense vegetation, likely using its strong, curved bill to dig into branches and leaf litter.^[5]

Clytoctantes alixii is thought to stay in the same area year-round, with no signs of migration.^[13] There is very little known about its diet, but one bird was seen near an army-ant swarm, and another was pulling apart dead plant stems, likely looking for insects.^[13] Its breeding habits are also mostly unknown, except that nesting occurs in the west half of the range between April and May.^[13] As for sounds, only a few recordings exist. One female in Colombia made a rough, buzzing call that sounded similar to that of Phaenostictus mcleannani.^[13]

Clytoctantes atrogularis mainly eats insects, especially ants, like other birds in the antbird family.^[3] It has been seen foraging in tangled vines and on bamboo, where it uses its strong bill to split open stems. It also searches for food around the base and coverings of certain palm leaves.^[3] This bird moves skillfully, climbing and moving sideways on branches.^[3] Stomach studies of a few samples show that it feeds mostly on ants, such as Camponotus, Pheidole, and Pachycondyla, as well as their eggs, including species that live inside bamboo.^[3] Males of Clytoctantes atrogularis sing a loud, clear song made up of evenly spaced whistled notes that can be heard from over 100 meters away.^[3] Both males and females make a short contact call, usually in a series of seven or eight notes.^[3] When alarmed, it gives a slightly chattering call with a faint squeaky tone.^[3]