There is little information on the reproductive biology of northern populations of Darwin's Nothura, apart from mention that breeding in Bolivia is in November-December (Cabot 1992). Breeding is reported in Argentina from early September (female specimen from 6 September with "ovaries developing"; Wetmore 1926) through the middle of March, although Bump and Bump (1969) suspected that there was little egg laying until October; the first nest they located was on 16 November, and the latest on 12 March.
Only the male constructs the nest, which is only a scrape on the ground, ca 2.5 cm in depth, and lined with grass and feathers, sometimes with a few twigs as well. The nest usually is very well concealed, hidden in clumps of vegetation, such as bunchgrass, that are ca 15-51 cm tall. The mean spacing of nests is not known, but two nests were located within 2 m (Bump and Bump 1969).
The eggs are chocolate brown to "deep wine", "with a suggestion of gray", and are unmarked (Bump and Bump 1969). Mean egg dimensions are 42.3 x 30.8 mm for nominate darwinii (n = 7 eggs) and 42.3 x 30.6 mm (n = 45 eggs) for salvadorii. The clutch size vary from three to nine, with a mean of six (Bump and Bump 1969). In captivity, up to three females lay eggs in a single nest, and presumably this applies to wild birds as well; the number of eggs per nest per female is not documented (Bump and Bump 1969). Egg fertility is high. In captivity, 7 from 48 eggs were infertile (Bump and Bump 1969).
Only the male incubates. Incubating males Male birds generally sit tight on the nest until very closely approached. Nest abandonment is unusual. The incubation period in captivity is 16-18 days. The male also cares for the young after hatching, until the young become independent after three to four weeks. The mean weight of the chicks at hatching is 13.9 g (Bump and Bump 1969).