Pale-legged Warbler

The pale-legged warbler is 13.5 cm (5.3 in) long and weighs 12.1 to 13.4 g (0.43 to 0.47 oz). The sexes have the same plumage. Adults of the nominate subspecies have a mostly olive-green head with dusky lores, a short yellow supercilium, a blackish stripe through the eye, a yellow crescent under the eye, and a yellow throat. Their nape, upperparts, wings, and tail are olive-green. Their underparts are yellow with a faint olive wash on the sides of the breast and flanks. Subspecies M. s. flavovirens is overall slightly brighter than the nominate and has a thin blackish edge along the top of the supercilium. Both subspecies have a dark iris, a blackish bill, and yellowish pink legs and feet. Juveniles have mostly dark brown upperparts with some olive tone on the wings and tail. Their underparts are a lighter, buffier brown. Their bill and legs are paler than adults'.

The pale-legged warbler's nominate subspecies is the more northerly of the two. One source places it in central Peru's Pasco and Junín departments. Another continues that range further south into the departments of Ayacucho and Cuzco but the cited survey does not state which subspecies was found there. Subspecies M. s. flavovirens is found from Cuzco south through Puno department and Bolivia into far northern Argentina's Jujuy and Salta provinces. Much doubt has been cast on a specimen from Colombia that was identified as this species; the species is not included in the list of Colombian bird species. The pale-legged warbler inhabits the interior and edges of humid montane forest, where it favors dense undergrowth along small watercourses and also stands of Chusquea bamboo. Sources differ slightly on its elevational range. One states it is mostly 1,800 to 3,050 m (5,900 to 10,000 ft) but is found as low as 1,500 m (4,900 ft) in Argentina. Another says it ranges between 1,700 and 2,900 m (5,600 and 9,500 ft) in Peru.

The pale-legged warbler's diet has not been studied but is assumed to be mostly or entirely invertebrates. It forages mostly in pairs or family groups, usually within about 2 m (7 ft) of the ground. It takes prey by gleaning from dense low undergrowth but also takes some prey on the wing. In the non-breeding season it sometimes joins mixed-species feeding flocks.