The Andean Swallow is endemic to the Andes, breeding in the high puna on cliffs and in roofs. The overall impression is of a dark, square-tailed swallow. It is a dark glossy blue on the upperparts, with a paler dusky gray-brown the rump, and pale gray-brown underparts. It is found above the elevational range of most swallow species, but may occur alongside the Blue-and-white Swallow (Pygochelidon cyanoleuca) and the Brown-bellied Swallow (Orochelidon murina).
Similar species found in the Andean Swallow's puna zone habitat are the Brown-bellied (Orochelidon murina) and Blue-and-white (Pygochelidon cyanoleuca) swallows. However, the Brown-bellied Swallow is uniformly dark below, has a more deeply forked tail, and a darker rump. The Blue-and-white Swallow is pure white on the throat, breast and belly, is bluer above, and the rump is the same color as the back. The juvenile Andean Swallow has a rusty (not grayish brown) rump, and so perhaps could be confused with the Cliff Swallow (Petrochelidon pyrrhonota), a rare migrant to the altiplano.
The following description is based on Turner and Rose (1989) and Fjeldså and Krabbe (1990):
A medium-sized swallow with a relatively short, notched or square tail.
Adult (sexes similar): Upperparts glossy blue-black (oroyae) or greenish-black (andecola); rump and uppertail coverts brownish (but may be concolor with the back in older individuals). Lores black; auriculars gray. Sides of the head, the chin, throat and breast gray-brown, shading to paler grayish white on the belly and undertail coverts. The flanks and the underwing coverts are gray-brown.
Juvenile: Plumage duller and browner. Tips to the tertials white, and tips of the greater wing coverts buffy. The rump is rufous-brown, and the uppertail coverts have a tawny tinge. Belly and undertail coverts are washed with pale rufous.
Data from Turner and Rose (1989):
Tarsi and toes: Horn-colored
Total length: 13.5 cm (Ridgely and Tudor 1989), 14 cm (Turner and Rose 1989, Fjeldså and Krabbe 1990, Jaramillo 2003).
Linear measurements from Turner and Rose (1989):
Wing length: mean 115.7 mm (range 113-122 mm)
Tail length: mean 56 mm (range 54-58 mm)
Bill length: mean 9.4 mm (range 8.8-9.9 mm)
Tarsus length: mean 11.3 mm (range 11.2-11.9 mm)
Mass: mean 17 g (range 14-19 g) (Turner and Rose 1989)