Southern beardless tyrannulet

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