The subspecies differ slightly in the intensity of the breast and uppertail covert colors and the size of the gular stripe.

[6] What was once thought to be a separate species P. fumosus was determined to be a melanistic morph of the nominate sooty-capped hermit.

[6] Active nests of the sooty-capped hermit have been found in Venezuela between February and July and also between September and December.

The nest is a cone-shaped cup; a typical one was made of moss and spider web with pieces of dried mud on the outer wall.

The sooty-capped hermit's song is "a continuously repeated phrase consisting of 2–3 high notes followed by 2–3 somewhat lower ones, e.g.

[6] The IUCN has assessed the sooty-capped hermit as being of Least Concern; though its population size is unknown it is believed to be stable.