Locally in eastern Andean foothills in north-central and south-eastern Ecuador (western Napo, Zamora-Chinchipe), north-central, central and south-eastern Peru (Amazonas, San Martín, Junín and Ayacucho south to Cuzco and Madre de Dios) and northern Bolivia (La Paz).
 
Population
Estimated population is unknown (2010).
Status VU
Habitat destruction and degradation from logging, mining, agriculture and road building, is the main threat.
For more information see BirdLife International Species Factsheet.
Food
Insects, fruits, including mistletoes.
Voice
An ascending series, beginning with an emphatic note and ending with a 'wheet-wheet?'.
Red-billed Tyrannulet (Zimmerius cinereicapilla) [XC863604]
by A. Bennett Hennessey from Sadiri Lodge, Bolivia (call, song)
Red-billed Tyrannulet (Zimmerius cinereicapilla) [XC70752]
by John V. Moore from Wildsumaco, 5km NW Guagua Sumaco, Napo, Ecuador (call)
Subspecies
No subspecies.
Despite superficial resemblance to Phyllomyias, genus appears to be more closely related to Phylloscartes. This species was formerly placed in a separate genus, Tyranniscus, but exhibits plumage and morphological features (wing pattern, proportionally long tail and bill, and derived characters of both syrinx and palate) typical of present genus.