Serra antwren

The serra antwren (Formicivora serrana) is a species of small insectivorous bird in subfamily Thamnophilinae of family Thamnophilidae, the "typical antbirds". It is endemic to southeastern Brazil.

Antwrens in the genus Formicivora have comparatively long tails, and the males are unusual in having underparts that are darker than the upperparts. The serra antwren is 12 to 14 cm (4.7 to 5.5 in) long and weighs 10 to 13 g (0.35 to 0.46 oz). Adult males of the nominate subspecies F. s. serrana have a white supercilium that extends down the neck, along the side of the breast, and widens and grays on the flanks. Their crown and upperparts are rufous-brown with white edges on the outer scapulars and a hidden white patch between them. Their wings are brownish black with white tips on the coverts, blackish bases on the flight feathers, and cinnamon-brown edges on the tertials. Their tail is black with white feather tips that increase in size from the central to the outer feathers. Their face, throat, and underparts are black with white underwing coverts. Adult females have a wide black band through the eye and their underparts are entirely creamy white.

Males of subspecies F. s. interposita and F. s. littoralis differ significantly from nominate males. Males of F. s. interposita have very dark brown to black upperparts, with a narrow and broken white supercilium, very small white tips on the wing coverts, and no white on the underparts. Males of F. s. littoralis also have very dark brown to black upperparts, with little or no supercilium, almost no white on the tail, no white on the underparts, and smaller white tips on the flight feathers than either of the other two subspecies. Females of subspecies F. s. interposita and F. s. littoralis are almost identical to each other. They differ only slightly from the female F. s. serrana by having pale buff (rather than creamy white) underparts.