Except for their voice, Yellow-crowned Tyrannulets are inconspicuous. These small flycatchers are common and widespread in humid lowlands, where they occur in river edge and disturbed forest, at forest edges, and clearings. Inside forest, they forage in the canopy, but often perch much lower at forest edges. Yellow-crowned Tyrannulets level, gleaning small fruit and insects during short sallies. Usually found as singles or pairs, they rarely join mixed flocks. Their call is a fairly low, whistled "too-pew", repeated incessantly throughout the day. Visually, Yellow-crowned Tyrannulets can be separated from similar species by their yellowish white wingbars, dark gray face, and stubby bill; the semi-concealed yellow crown is difficult to see in the field.