Breeding: In Goiás, Brazil, breeding occurs between September-November, while in São Paulo, Brazil, breeding occurs in November (Isler and Isler 1999). At a site in Brazil, Santos (2008) observed the breeding season to last from mid-August to the beginning of December. White-rumped Tanagers build cup nests 1-2 m above the ground in forked branches (Isler and Isler 1999). The nests are made from tightly woven grass, sometimes including leaves or twigs, and are lined with a cotton-like plant material from Eriotheca (Isler and Isler 1999). At a site in Brazil, Santos (2008) observed 64 nests, which were placed 3.7 ±0.3 m above the ground. The most commonly used plants for nest placement were trees in the genus Kilemeyera, but 15 other species were used as well. Nest measurements were as follows: height: 61.2 ± 2.5 mm; external diameter: 86.8 ± 3.4 mm; internal diameter: 61.7 ± 1.9 mm.
Eggs: Isler and Isler (1999) list the typical clutch size as four, rarely three. Santos (2008) observed a clutch size from one to three. The eggs are ovoid in shape and colored pale blue with black or dark brown spots that form a wreath around the large end (Isler and Isler 1999, Santos 2008). Egg weight averages 3.0 ± 0.1 g, length averages 20.6 ± 0.7 mm and width averages 15.5 ± 0.05 mm (n=26, Santos 2008).
Parental care, condition at hatching, growth and development, brooding, feeding, etc: White-rumped Tanagers typically employ helpers (one or two birds) at the nest, which are possibly young from the previous breeding season (Isler and Isler 1999, Santos 2008). Females lay the eggs asynchronously. The female alone incubate eggs , while males and helpers guard the nest (Santos 2008). The incubation period lasts 16 ± 0.3 days, and the nestling period lasts from 12.1 ± 0.5 days (Santos 2008). All individuals in the group (male, female, and helpers) feed the young (Santos 2008). Of the nests studied by Santos (2008), 32.7% were successful, 56.9% were depredated, and 10.4% were abandoned.