There is surprisingly little information on the reproductive biology of Short-tailed Antthrush, in view of the extensive distribution of this species.
Nests with eggs are reported from September in Paraguay (Bertoni 1901) and in Argentina (Maders and Matuchaka 2011), and from November in southern Brazil (Franz 2013); male specimens collected in Rio Grande do Sul, southern Brazil, between 18 September-1 December had enlarged testes (Belton 1985). The only known nest from the Andes was encountered in northeastern Ecuador, and contained nestlings (Greeney and Gelis 2007). Nests of Short-tailed Antthrush as placed in cavities in live trees. The few described nest sites are 1-3 m above the ground (Bertoni 1901, Maders and Matuchaka 2011, Franz 2013). The entrance to the nest in Argentina was a vertical slit (Maders and Matuchaka 2011). The nest in southern Brazil was in a natural cavity of a 5 m tall, live tree (Allophylus edulis, Saplindaceae), with a cavity entrance that was vertical and irregular, and measured 9.5 x 12.5 cm; the bottom of the cavity entrance was 151 cm above the ground. The incubation chamber at the bottom of the cavity had an internal diameter of 11.5 x 9.5 cm. This nest contained three white, unmarked eggs, which rested on a "bed" of green leaves, 1.5 cm deep. Nestlings a few days old have pink skin and are covered in a blackish gray down (Maders and Matuchaka 2011, Franz 2013). Pin feathers develop somewhere between the age of 9-12 days (Franz 2013). Franz (2013) estimated the nestling period as 16-19 days.