Only one nest of Yellow- breasted Antpitta has been described (Greeney et al. 2009), and the following details are taken from that nest in northwestern Ecuador. As with other species of Grallaria (Greeney et al. 2008) the nest was a bulky, relatively deep, open cup structure. It was composed mostly of green moss and fern leaves intermixed with a few sticks, leaf rachises and vines. The nest was lined with dark rootlets and a few bare fern rachises. It was situated 1.5 m above ground and built against the side of an epiphyte-laden tree trunk. These epiphytes partially shaded and provided the majority of support for the nest. Externally, the cup was ca 20 cm in diameter and 15 cm tall. The internal egg cup was 13 cm wide by 12 cm front to back, and 7.5 cm deep. When first discovered the nest contained two turquoise eggs which may have been lightly spotted, but they were not examined closely. Nestlings of Yellow-breasted Antpitta, estimated to be about a week old, weighed 29.8 and 32.7 g. They were pale- skinned with patches of black down on the dorsum. Their primary feathers were not yet broken their sheaths. Their mouth linings and gape were bright crimson- orange.
There are too few data to accurately define the breeding season of Yellow-breasted Antpitta. The nest described above contained eggs on 20 January, the rainy season in that area (Greeney and Nunnery 2006). Also in northwestern Ecuador, Roger Ahlman informed me of a juvenile coming to the worm feeding station at Refugio Paz de las Aves near the end of September. Although plumage transitions are not fully known for Yellow-breasted Antpittas, I believe this juvenile to have left the nest sometime in March or April of that year. This previously unpublished record agrees with wet-season breeding in northwest Ecuador. The only other information on seasonality involves breeding condition specimens collected in June in Colombia (Hilty and Brown 1986) and a pair showing "precopulatory" behaviors in March in Cauca (Negret 1997).