About Serpophaga griseicapilla Straneck, 2007
Straneck's tyrannulet (Serpophaga griseicapilla) measures 9 to 11 cm (3.5 to 4.3 in) in length and weighs 4.4 to 7.5 g (0.16 to 0.26 oz). Both sexes share identical plumage. Adults have a gray crown and nape, with a small hidden patch of white on some black feathers in the center of the crown. They have a thin white supercilium, a white crescent below the eye, and a dark gray line running through the eye, on an otherwise grayish white face. Their upperparts are olivaceous brown. Their wings are dusky brownish gray, with lighter edges on most flight feathers and two wing bars that range in color from cinnamon to whitish. Their tail is dark gray-brown, with whitish edges on the outermost feathers. Their chin and throat are white with a faint grayish wash. Their breast is grayish, fading to pale yellow on the belly. Both sexes have a hazel-brown to dark brown iris, a black bill, and black legs and feet. Different taxonomic systems report different ranges for Straneck's tyrannulet. According to the South American Classification Committee of the American Ornithological Society, the species breeds in Argentina and Bolivia, and is a non-breeding visitor to Brazil, Paraguay, and Uruguay. The range map from BirdLife International (BLI), which is used by the IUCN, shows the species breeding only in Argentina, and occurring as a non-breeder in northern Argentina, southern Bolivia, far southern Brazil, Paraguay, and Uruguay. The International Ornithological Committee generally agrees with BLI but raises questions about the species' presence in Brazil. The Clements taxonomy does not include Bolivia in its statement of the species' range; it lists the other four countries but does not specify whether the species occurs there as a breeder or non-breeder. The Cornell Lab of Ornithology's Birds of the World describes the species as breeding in northwestern Argentina and possibly southern Bolivia, and occurring 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 from Bolivia came from 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. It occurs at elevations between approximately 30 and 2,280 m (100 and 7,500 ft).
