Rather, they spend much time guarding their mates during this time to prevent them from mating with other males. Eggs can be laid as early as late March or as late as early June, depending upon the weather and latitude. Females may begin to lay eggs one or two days after the nest is completed, but some females wait a week or more. 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.