# Southern beardless tyrannulet

The southern beardless tyrannulet (Camptostoma obsoletum) is a small passerine bird in subfamily Elaeniinae of family Tyrannidae, the tyrant flycatchers. It is found in Costa Rica, Panama, in every mainland South American country except Chile, and on Trinidad.

## Taxonomy and systematics

The southern beardless tyrannulet has these 13 subspecies:
* C. o. flaviventre Sclater, PL & Salvin, 1865
* C. o. orphnum Wetmore, 1957
* C. o. majus Griscom, 1932
* C. o. caucae Chapman, 1914
* C. o. pusillum (Cabanis & Heine, 1860)
* C. o. napaeum (Ridgway, 1888)
* C. o. maranonicum Carriker, 1933
* C. o. olivaceum (Berlepsch, 1889)
* C. o. sclateri (Berlepsch & Taczanowski, 1884)
* C. o. griseum Carriker, 1933
* C. o. bolivianum Zimmer, JT, 1941
* C. o. cinerascens (Wied-Neuwied, M, 1831)
* C. o. obsoletum (Temminck, 1824)
Several authors have suggested that the southern beardless tyrannulet may be composed of more than one species. Genetic evidence suggests that as many as three may be present. The Clements taxonomy divides the subspecies into two groups within the species. The northern (pusillum) group includes the seven subspecies C. o. flaviventre through C. o. olivaceum in the above list and the southern (obsoletum) group includes the other six.
The southern beardless tyrannulet shares genus Camptostoma with the northern beardless tyrannulet (C. imberbe); they have at times been considered conspecific and together they form a superspecies.

## Description

The southern beardless tyrannulet is 9.5 to 10.5 cm (3.7 to 4.1 in) long and weighs 7 to 9 g (0.25 to 0.32 oz). It is a small flycatcher with a long pointed warbler-like bill. The sexes have the same plumage. Adults of the nominate subspecies C. o. obsoletum have a grayish crown and nape; the crown feathers are often bushy with dark centers. They have white lores and a broken white eyering on an otherwise grayish white face. Their upperparts and tail are medium olive-gray. Their wings are dusky with whitish to creamy edges on the inner flight feathers. Their wing coverts have cinnamon tips that show as two wide bars on the closed wing. Their throat is grayish white and the rest of their underparts mostly pale yellow with a faint olive wash on the breast. Juveniles are duller and browner than adults with pale buffish white underparts. Both sexes of all subspecies have a brown iris, a horn-colored maxilla, a dull orangish or pinkish mandible, and gray legs and feet.
The other subspecies of the southern beardless tyrannulet differ from the nominate and each other thus:
* C. o. flaviventre: warm grayish olive upperparts with somewhat darker crown, creamy white wing bars and inner flight feather edges, and deep yellow underparts
* C. o. orphnum: smallest subspecies, with very dark crown
* C. o. majus: similar to flaviventre but grayer overall with less contrasty crown
* C. o. caucae: drab grayish olive upperparts with darker crown, creamy white to pure white wing bars, and very pale yellow underparts with distinct grayish to grayish olive cast to the breast
* C. o. pusillum: like caucae but slightly smaller
* C. o. napaeum: similar to caucae and pusillum but slightly darker olive
* C. o. maranonicum: smaller and much paler than nominate, with slightly olive gray-brown upperparts, cinnamon-buff tinge to wing bars and inner flight feather edges, and creamy white underparts with a warm gray cast to the breast
* C. o. olivaceum: dark olive crown, olive upperparts, pale yellow-green to whitish wing bars, bright yellow-green edges to inner flight feathers, and bright yellow underparts
* C. o. sclateri: smaller and paler than nominate though somewhat darker than maranonicum and with dull cinnamon uppertail coverts
* C. o. griseum: smaller and paler than nominate though somewhat darker than maranonicum
* C. o. bolivianum: slightly larger than nominate
* C. o. cinerascens: like nominate with slightly paler underparts

## Distribution and habitat

The subspecies of the southern beardless tyrannulet are found thus:
* C. o. flaviventre: Pacific slope of Costa Rica and both slopes of Panama
* C. o. orphnum: Coiba Island off southwestern Panama
* C. o. majus: Pearl Islands off southern Panama
* C. o. caucae: Colombia on western slope of the Western Andes, in the Cauca River and upper Magdalena River valleys, and on eastern slope of the Eastern Andes
* C. o. pusillum: Trinidad, Caribbean coast and lower Magdalena valley of Colombia, and northern Venezuela east to Sucre and south to Apure and northern Amazonas states
* C. o. napaeum: from Amazonas and southeastern Bolívar states in Venezuela east across the Guianas and northern Brazil to the Atlantic in Amapá and Pará states
* C. o. maranonicum: Peru in eastern Piura Department and the middle valley of the Marañón River in Amazonas, Cajamarca, and Ancash departments
* C. o. olivaceum: from southeastern Colombia south through eastern Ecuador into eastern Peru to central Ucayali and east into western Amazonas state of Brazil south of the Amazon
* C. o. sclateri: western Ecuador and south into Tumbes and northern Piura departments in far northwestern Peru
* C. o. griseum: Pacific coast and slope of western Peru between Lambayeque and Lima departments
* C. o. bolivianum: eastern slope of the Andes from central Bolivia south into northwestern Argentina to Tucumán Province; migrant to southeastern Peru
* C. o. cinerascens: eastern Brazil roughly bounded by Maranhão, Ceará, Espírito Santo, and central Mato Grosso states and into Bolivia's eastern Santa Cruz Department
* C. o. obsoletum: from southern Mato Grosso to Rio de Janeiro state in southern Brazil south to Paraguay, Uruguay, and northeastern Argentina as far as La Pampa and northern Buenos Aires provinces
The southern beardless tyrannulet is found in almost every habitat available in its range. These include desert with cactus, thorn-scrub, deciduous and gallery forest, the edges of humid forest, secondary forest, edges along watercourses and oxbow lakes, and parks and gardens in built-up areas. It generally shuns the interior of continuous humid forest but occasionally occurs in várzea and swamp forests. In elevation it reaches 1,200 m (3,900 ft) in Costa Rica, 750 m (2,500 ft) in Panama, 1,500 m (4,900 ft) in Colombia, 2,800 m (9,200 ft) in western and mostly to 300 m (1,000 ft) in eastern Ecuador, 2,600 m (8,500 ft) in Peru, 1,000 m (3,300 ft) in Venezuela, and 2,000 m (6,600 ft) in Brazil.

## Behavior
### Movement

The southern beardless tyrannulet is a year-round resident in almost its entire range. Part of the southern population moves northwest into southeastern Peru in the austral winter.

### Feeding

The southern beardless tyrannulet feeds mostly on insects and spiders; berries such as those of mistletoe (Loranthaceae) and other small fruits are also a significant part of its diet. It usually forages alone or in pairs and occasionally joins mixed-species feeding flocks. It forages actively, moving frequently as it gleans prey and fruits from a perch; it occasionally takes food while briefly hovering. It feeds mostly in the crown of trees and the upper parts of lower vegetation though west of the Andes it often feeds at any level of the forest.

### Breeding

The southern beardless tyrannulet's breeding season varies widely across its range, for instance between December and March in Central America, September to December in Suriname, and August to January in Argentina. The female alone builds the nest, a bulky globe with a side entrance made of a variety of plant materials, spider web, and cocoon cases and lined with seed down and other fine materials. It can be placed from just above the ground to as high as 30 m (100 ft) high in a tree and is typically well hidden. In a study in Ecuador, 12 of 20 nests were placed near an active wasp nest. The clutch is usually two eggs and rarely three. The incubation period is 14 to 15 days and fledging occurs about 17 days after hatch. Both parents provision nestlings.
* Songs and calls
* Listen to the southern beardless tyrannulet on xeno-canto

### Vocalization

The southern beardless tyrannulet has a variety of vocalizations. They include a "[t]hin, high whistle, 'fleeeeer', rising and falling slightly, sometimes with terminal syllables, 'fleeeeee-pit-pit' " and a "descending series of clear, minor-key notes, 'fleee, flee-fleew-fleew' ". When calling it often raises its crest. The species is highly responsive to recordings of the local species of pygmy owl, coming close and calling and fussing.

## Status

The IUCN has assessed the southern beardless tyrannulet as being of Least Concern. It has an extremely large range and its estimated population of at least 50 million mature individuals is believed to be stable. No immediate threats have been identified. It is considered fairly common to very common in most of its range. It is considered rare at the northern end of its Costa Rican range, less numerous is eastern Ecuador than western, and uncommon in northeastern Peru. "Preference for scrub, lighter woodland and semi-open habitats makes it less susceptible to forest degradation and disturbance than are many other tyrannids; able to exploit converted habitats."