Breeding

Despite the wide geographic range and abundance of Bright-rumped Yellow-Finch, there is very little information on its reproductive biology. Morrison (1939b) reported breeding at Lake Junín in central Peru in February and March. The only completely described nest was found in February in northern Argentina (de la Peña 1987). Eggs are reported from central Peru in May and June; nestlings from southern Peru in April and May; and fledglings from April to August in Peru and Bolivia (Fjeldså and Krabbe 1990).

Morrison (1939b) described the nest site as "at the end of a quite long tunnels made in dry places", but did not describe the nests themselves. Morrison (1939b) further supposed the these nests originally were excavated by miners (Geositta). Nest sites also are described as "in rocky sites, between stones or in burrows in the ground" (Koepcke 1970) and as "on rocky slopes with scattered shrubs, in stone fences, burrows in the ground or under roofs" (Fjeldså and Krabbe 1990). The only nest reported in detail is one described by de la Peña (1987): the nest was a small cup at the end of a short tunnel 30 cm above the ground in a mud fence.

The clutch is four (n = 1; de la Peña 1987). The eggs are white with chestnut and gray speckling and spotting, more heavily marked around the larger end (de la Peña 1987). Egg dimensions are 20-21.3 x 14.9-15.3 mm (n = 4, single clutch; de la Peña 1987). The length of incubation or the nestling period are not known.