Crowned Slaty Flycatcher nests with eggs have been recorded from November to early January, and nestlings from mid-December to early January. Nests are more or less round to oval and cup-shaped with an external diameter ca 12-16 cm and height 5-7 cm, often loosely constructed. There is a shallow egg chamber ca 7-8 cm wide and 3-5 cm deep. The nest is primarily composed of smaller twigs (generally ca 2-3 mm thick, occasionally some pieces as large as 10 cm) and leaf stems, lined with rootlets and grass. The nest is usually placed in the fork of a horizontal tree branch ca 2-6 m above ground and often fairly close to the trunk, but also as much as 2 m from the main bole (Barrows 1883, Friedmann 1927, Mobley 2004).
Clutch size is 2-3 eggs, sometimes 4, laid on consecutive days (Friedmann 1927). The eggs are pale cream, spotted with purplish brown, and are more densely marked around the larger end (Friedmann 1927, Smyth 1928). Representative samples of the dimensions of the eggs are 19.5-21.5 mm x 14.5-15.5 mm (Smyth 1928); and mean 21 x 15.8 mm (range 20.2-21.8 mm x 15.7-16.4 mm, n = 8; de la Peña 1987). The incubation period is ca 15-16 days and the nestling period c. 16 days (Mobley 2004). The nests sometimes are parastized by Shiny Cowbird Molothrus bonariensis (Friedmann et al. 1977, Friedmann and Kiff 1985).