Ultramarine Grosbeaks are mostly sedentary, moving only short distances. They are commonly seen foraging for seeds and fruits, often close to the ground or up to two meters high in the vegetation. Males are known for their melodious singing, particularly during the breeding season. Both parents participate in nest building, incubation, and chick feeding.

This species thrives in secondary forests, forest edges, and clearings. Our study was conducted around the Pedra Talhada Biological Reserve in northeastern Brazil — a transitional zone between the Atlantic Forest and Caatinga ecosystems.

We observed nests in northeastern Brazil, particularly in Alagoas state (23 nests).

In the study area, nesting occurred from February to September. In other Brazilian states, breeding can take place nearly year-round. In Argentina, nesting typically occurs between late October and early February.

The Ultramarine Grosbeak builds cup-shaped nests with thin walls made of roots, tendrils, and leaf stalks, placed at the fork of small branches. They were usually placed in forest-edge vegetation or on rocky outcrops, between 0.8 and 5.2 m above the ground in Alagoas. Common nesting plants included Psidium guineense, Vitex polygama, and Cnidoscolus urens.