Cosmopsarus regius exhibits cooperative breeding, where group members assist with nest-building and the feeding of the young. Breeding females often solicit food from other members of the group to feed to the young by assuming a crouched position, quivering their slightly raised wings, gaping and vocalizing. Members respond either by ignoring her and feeding the young directly, giving her part of the food and feeding the remainder to the young, or giving her all the food. Unlike most starlings which feed on a combination of insects and fruits, the Golden-breasted starling lives almost entirely on insects. Termites are caught by opening their ground tunnels with rapid flicks of its bill and other insects are caught in flight.
Literature also suggests it eats snails, crabs, spiders and small vertebrates.
The Golden-breasted starling nest in tree holes, often abandoned by, or usurped from, woodpeckers, and sparsely line it with straw, leaves or roots. Clutch sizes is 3 to 5 eggs. The eggs are elongated, pale greenish-blue with reddish brown specks and about 1.1 x 0.7 inches. Like most starlings, C. regius molts once a year, after the breeding season. The life expectancy of the Golden-breasted starling is 1.2 to 1.4 years.