Straneck's Tyrannulet

Straneck's tyrannulet is 9 to 11 cm (3.5 to 4.3 in) long and weighs 4.4 to 7.5 g (0.16 to 0.26 oz). The sexes have the same plumage. Adults have a gray crown and nape with a hidden bit of white on some black central crown feathers. They have a thin white supercilium, a white crescent under the eye, and a dark gray line through the eye on an otherwise grayish white face. Their upperparts are olivaceous brown. Their wings are dusky brownish gray with lighter edges to most of the flight feathers and two cinnamon to whitish wing bars. Their tail is dark gray-brown with whitish edges on the outer feathers. Their chin and throat are white with a grayish wash. Their breast is grayish that progresses to pale yellow on the belly. Both sexes have a hazel-brown to dark brown iris, a black bill, and black legs and feet.

Taxonomic systems differ on the range of Straneck's tyrannulet. According to the South American Classification Committee of the American Ornithological Society, it breeds in Argentina and Bolivia and is a non-breeding visitor to Brazil, Paraguay, and Uruguay. BirdLife International's (BLI) map, used by the IUCN, shows it as breeding only in Argentina and as a non-breeder in northern Argentina, southern Bolivia, far southern Brazil, Paraguay, and Uruguay. The International Ornithological Committee generally agrees with BLI but questions Brazil. The Clements taxonomy does not include Bolivia in its range statement; it lists but does not specify breeding or non-breeding in the other four countries. The Cornell Lab of Ornithology's Birds of the World describes it as breeding in northwestern Argentina and possibly southern Bolivia and as a non-breeder in eastern Bolivia, southern Brazil, Paraguay, and Uruguay. During the breeding season Straneck's tyrannulet inhabits the Monte Desert in Argentina. One apparent breeding-season record in Bolivia was in the Gran Chaco, a dry forest biome. In its non-breeding range it inhabits the Chaco, the Argentine Espinal, Pampas grasslands, and lowland moist forest. In elevation it occurs between about 30 and 2,280 m (100 and 7,500 ft).

Straneck's tyrannulet feeds on arthropods. It moves through vegetation with short jumps and flutters, feeding from very near the ground up to at least 6 m (20 ft) above it.