All five species of tody (Todus) are very small, chunky, short-tailed birds, with green upperparts, a red throat, and a long, flattened bill. The Narrow-billed Tody is mostly white below, with pinkish red flanks and yellow lower belly and undertail coverts.
The Narrow-billed Tody is similar to the Broad-billed Tody (Todus subulatus), Cuban Tody (Todus multicolor), Jamaican Tody (Todus todus), and Puerto Rican Tody (Todus mexicanus). Of these species, however, the Narrow-billed Tody overlaps geographically only with the Broad-billed Tody. Broad-billed Tody usually is yellower on the breast, and the mandible is entirely red; Narrow-billed Tody is whiter on the breast, and the mandible usually is tipped with black. The two species also differ by voice, which often is the best way of differentiating them in the field.
The Narrow-Billed Tody resembles the Cuban Tody (Todus multicolor) in plumage, but does not have yellow lores or blue on its neck (Kepler 1977). Its bill is approximately one half the bill width of the Broad-billed Tody (Todus subulatus) and approximately one third the bill widths of the other tody species (Kepler 1977). The following detailed description is based in Ridgway (1914):
Information needed. Contribute
Adult: Sexes similar. Upperparts bright green, brighter (almost emerald green) in orbital region and forecrown. Malars white. Chin and throat deep carmine red; most of the throat feathers, however, have a minute, terminal white dot. Sides of neck and breast, and posterior end of malar region, deep plumbeous gray. Breast and belly white, the breast sometimes faintly tinged with gray. Flanks geranium red or deep geranium pink. Undertail coverts, axillars, and underwing coverts clear sulphur yellow.
Data from Ridgway (1914):
Bill: maxilla black, becoming more brownish distally; mandible red, dusky distally
Linear measurements (mm) of Todus angustirostris (Ridgway 1914)
| || wing length || tail length || bill length || bill width || tarsus || n |
| || || || (exposed culmen) || (at nostrils) || || |
| male || mean 45.3 || mean 34 || mean 18.1 || mean 4.4 || mean 14.3 || 10 |
| || range 43.5-46 || range 32.5-35.5 || range 17.5-18.5 || range 4-5 || range 13.5-15 || |
| female || mean 43.9 || mean 32.5 || mean 17.6 || mean 4.2 || mean 14.1 || 9 |
| || range 42-45.5 || range 31-35 || range 16.5-19 || range 4-4.5 || range 13.5-15 || |
Mass: mean 7.5 g (range 6.5-9 g, n=6, sexes combined; Arendt et al. 2004).