About Cnemarchus erythropygius (P.L.Sclater, 1853)
The red-rumped bush tyrant, Cnemarchus erythropygius, measures 20 to 23 cm (7.9 to 9.1 in) in length; one recorded female weighed 50 g (1.8 oz). Males and females share the same plumage pattern. Adults of the nominate subspecies have a white forecrown that transitions to a hoary gray crown. Their back is dark gray brown, and their rump is rufous. Their wings are dark gray brown, with extensive white markings on the tertials that form a noticeable patch when the bird is in flight. Their central tail feathers are blackish, while the remaining tail feathers are rufous with blackish coloring on the outer quarter of their length. The chin and throat are white with thin dusky streaks. The breast is gray, fading to rufous on the belly and undertail coverts. Subspecies C. e. orinomus has a grayer back than the nominate subspecies, with a brown rump. Its tail feathers have less black on the tips, and its belly is paler than that of the nominate. Both subspecies have a brown iris, a black bill, and black legs and feet. The red-rumped bush tyrant has a disjunct distribution that occurs mostly in the Andes. The nominate subspecies ranges from Nariño Department in southwestern Colombia, south through Ecuador and Peru, to Cochabamba Department in Bolivia. Subspecies C. e. orinomus is found in Colombia, in the isolated Sierra Nevada de Santa Marta in the north, and in the Eastern Andes of Norte de Santander and Cundinamarca departments. This bird inhabits grassy and shrubby paramo biome and Polylepis groves. Its elevational range is 3,100 to 4,000 m (10,200 to 13,100 ft) in Colombia, 2,850 to 4,100 m (9,400 to 13,500 ft) in Ecuador, 3,000 to 4,300 m (9,800 to 14,100 ft) in Peru, and 3,100 to 4,300 m (10,200 to 14,100 ft) in Bolivia.
