The diet of the rose-breasted grosbeak varies between seasons, with a higher percentage of insect prey, including beetles, ants and butterfly and moth larvae, being taken during the breeding season. In winter, a higher percentage of seeds, fruits and buds are taken, including elderberries, blackberries, raspberries and weed seeds. Some plant material is also eaten in the breeding season (2).
At the beginning of the breeding season, the female rose-breasted grosbeak approaches a singing male, who in turn performs a courtship display involving flight, positioning and song. The pair is monogamous and builds a nest between May and June, with egg laying generally occurring between mid-May and July (2). The nest of the rose-breasted grosbeak is a loose, open cup-shaped structure, and is made from sticks, grass, weeds, decayed leaves and straw, lined internally with fine sticks, roots and hair (3) (2).
A single clutch of 1 to 5 eggs is incubated by both the male and female rose-breasted grosbeak for 12 to 13 days (2), although the female spends most time on the nest, especially at night (2) (3). The smooth-surfaced eggs are slightly glossy and are pale green, blue or green-blue in colouration, with red-brown and purple-red spotting. The young are fed insect matter by both adults and may fledge the nest just nine days after hatching, although fledging at around ten days is more common. The young are dependent on the adults for around three weeks after fledging, with family groups being maintained until migration occurs at the end of the summer (2).
During the breeding season, the male and female rose-breasted grosbeak are intolerant of other individuals and are often involved in conflicts when defending their territory. However, during winter and migration this species is relatively gregarious, forming flocks of up to 50 birds (2).
The northward migration of the rose-breasted grosbeak from its wintering grounds begins between mid-March and mid-April, with individuals arriving on the breeding grounds until late May. Male rose-breasted grosbeaks usually arrive and establish a nesting territory first, with females arriving later. By mid-September, migration begins back to the wintering grounds, with the birds arriving between late October and early November. Migration usually takes place at night (2).