The timing of breeding in Blackish Nightjar varies across its range, but typically is concentrated in the long dry season from August to October (Jackson and Ingels 2010). In French Guiana and Suriname specifically, breeding occurs during the short the dry season (February-March) and the long dry season (August to November). Occasionally eggs are found during rainy seasons (Solano-Ugalde et al. 2012).
A single 25 mm egg is occasionally laid in open sandy, gravelly, or bare soil, sometimes with leaf litter or few twigs. Most frequently, however, eggs are laid in depressions on bare granite rock, with no true nest (Ingels et al. 1984, Cleere and Ingels 2002, 2004, Solano-Ugalde et al. 2012). Blackish Nightjars nest semi-colonially with up to 20 pairs in 5 ha, but will also nest solitarily (Jackson and Ingels 2010). Egg coloration is variable, but usually glossy, creamy-buff and lilac color with brown to black spots and blotches. Eggs range in size from 23.9-27.7 mm x 17.2-20.6 mm. Incubation is likely 17-22 days long (variable depending on local, perhaps due to local overnight temperatures) and this responsibility is shared by male and female (Cleere and Ingels 2002, 2004, Solano-Ugalde et al. 2012). Adults do not remove eggshell after hatching (Cleere and Ingels 2004, Solano-Ugalde et al. 2012). Chicks are semi-precocial; from the first day chicks can move several meters by hopping (Ingels et al. 1984). Fledging occurs around day 14 and young disperse from the nesting area at 16-18 days old (Cleere 1998). Blackish Nightjar is thought to double brood and produce two clutches annually (Jackson and Ingels 2010).
Observations suggest that failure of a first egg induces egg replacement (Cleere and Ingels 2004, Solano-Ugalde et al. 2012). Eggs are more vulnerable than chicks with loss of eggs being three times higher than loss of hatched young. The average total nesting success thought to be 28 +/- 15% (Ingels et al. 1984).
Chicks are usually grayish brown in color with slightly darker backs, however two beige-cream colored chicks have been documented in Ecuador (Jackson and Ingels 2010, Solano-Ugalde et al. 2012).