Appearance

Serpophaga are small tyrant flycatchers with short tarsi and plumage that is predominately gray, and have a semiconcealed white patch on the crown. Torrent Tyrannulet is mostly pale gray, with a paler belly and a whitish throat, contrasting with a dark slaty crown and sides of the head, and blackish wings and tail.

Torrent Tyrannulet is distinctive in plumage, habitat, and behavior, and is unlikely to be mistaken for other species. River Tyrannulet (Serpophaga hypoleuca) of Amazonia usually occurs at lower elevations than Torrent Tyrannulet, and the two species are not likely to occur together. River Tyrannulet is even smaller than Torrent Tyrannulet, is browner above, and has paler wings and tail. Black Phoebe (Sayornis nigricans) overlaps extensively with Torrent Tyrannulet in geographic distribution and in habitat preference, but Black Phoebe is much larger and is mostly black.

The following description is based on Wetmore (1972) and Fitzpatrick (2004):

Adult male: Crown, sides of head, and nape black, with a semiconcealed white patch in the center of the crown. Back, scapulars, rump, and uppertail coverts gray. Lesser wing coverts slate black, feathers edged with gray; median and greater coverts black, feathers edged with grayish white; remainder of wing black. Rectrices black, feathers sometimes indistinctly tipped with grayish white. Chin and throat grayish white. Breast and flanks pale gray. Center of breast and belly white; undertail coverts and tibial feathers slightly grayish.

Adult female: Very similar to adult male, but crown and hindneck slightly duller black; white crown patch reduced or lacking.

Juvenile: Crown dusky, mixed with dull gray. Upperparts brownish gray, darker on the uppertail coverts.

The Torrent Tyrannulet's molting cycle has not been documented; it is likely, however, to follow the complex basic strategy like most passerines without alternate plumages.

Iris: dark brown

Bill: black

Tarsi and toes: black

Inside of mouth (including the tongue) orange.

Bare parts color data from Wetmore (1972).

Total length: 9.5-10.5 cm (Wetmore 1972), 10 cm (Stiles and Skutch 1989), 11.4 cm (Hilty 2003), 11.5 cm (Ridgely and Tudor 2009)

Linear measurements: 

male (n = 10, grisea; Wetmore 1972): wing length, mean 51.9 mm (range 50.1-53.5 mm); tail length, mean 40.1 mm (range 36.0-43.4 mm); culmen from base, mean 10.6 mm (range 10.2-11.0 mm); tarsus, mean 16.1 mm (range 15.3-16.5 mm)

female (n = 10, grisea; Wetmore 1972): wing length, mean 50.1 mm (range 48.0-51.7 mm); tail length, mean 38.1 mm (range 36.0-41.4 mm); culmen from base, mean 10.2 mm (range 9.4-11.0 mm, n = 9); tarsus, mean 16.1 mm (range 15.8-16.5 mm)

Mass: mean 8.3 g (n = 8; Dunning 2008).