One egg is laid each day, in the morning. The average clutch has three to five eggs but as many as seven have been reported. Clutch sizes tend to be smaller for younger females and for second broods of the breeding season. The eggs are smooth and glossy and are sky blue or white in color. Because all eggs laid by a single female are the same color, the presence of an odd-colored egg in a clutch may indicate that another female has laid her egg in the nest, a practice known as egg dumping.
Females generally begin to incubate the day the last egg is laid.
The incubation period is 12 to 14 days but can be longer in the case of extreme or prolonged cold weather. Both adults tend the young. The nestlings begin to thermoregulate, or regulate their own body temperatures, when they are about six days old, and females then decrease the amount of time they spend brooding. Nevertheless, the females may continue to brood at night during cold weather. The young leave the nest after 16 to 22 days, but they remain dependent upon their parents for food and protection for three to four weeks.