Breeding (active nests) is reported from February in Tocantins (Biancalana et al. 2012),from December-January in Minais Gerais (Vasconcelos et al. 2006), from November-February in Paraná (Pichorim et al., cited by Vasconcelos et al. 2006), and November-January in Misiones (Pearman et al. 2010). Breeding also is reported from September-March in Rio de Janeiro (Fichberg et al., cited by Vasconcelos et al. 2006); specimens collected in Rio Grande do Sul in October and November were in breeding condition (Belton 1984).
Nests are a cup or crescent-shaped structure composed of fern stems, rootlets, moss, leaves, soil, pebbles, and mud (Vasconcelos et al. 2006, Pearman et al. 2010, Biancalana et al. 2012). Most nests are on natural ledges in cliff walls, but some are attached directly to a cliff wall; the means of this attachment is unknown. The height of the above the ground ranges from ir nest on the cliff wall differs greatly ranging from 1.5-60 m (Vasconcelos et al. 2006, Pearman et al. 2010, Biancalana et al. 2012). These birds tend to nest as close to waterfalls as they possibly can without getting the nest wet, whether the waterfall is in a small cave or it is a large one in a river (Pearman et al. 2010). The clutch is a single white egg (Vasconcelos et al. 2006, Pearman et al. 2010, Biancalana 2012).
The descriptions of the nest and eggs of Sooty Swift by Dabbene (1918) refer to Rothschild's Swift (Cypseloides rothschildi), not Sooty Swift.