The female builds her nest alone. After constructed the external structure, she forms the cavity from the inside by turning her body and pushing out her feet. Cardinal nests are highly susceptible to cowbird nest parasitism, a process in which a female cowbird lays her eggs in the nest of another bird after dumping the eggs of the host bird over the side. The host, in this case a female cardinal, will then incubate and hatch the cowbird eggs and raise the cowbird fledglings. If left alone, the female cardinal will lay three or four eggs within a week of completing the nest.
Cardinal eggs are glossy light green or dull gray, with reddish brown specks or blotches.
The female incubates the eggs in solitude for 13 days before they hatch. At that point, the fledglings are covered with gray down. Fledgling cardinals can fly well within 20 days, but they seldom venture far. Nonmigratory and territorial, a cardinal may spend its entire life within a half-mile of its birthplace. Cardinals eat a large number of seeds and insects.