Doing so could result in the nestlings leaving the box before they are able to fly, greatly reducing their chance of survival. Pine needles may be used. Always remove house sparrow nests immediately. However, boxes may also be put up later in the nesting season. Bluebirds usually nest in late March or early April, depending on weather conditions.
Bluebirds usually have two broods per season, but three broods are possible.
Bluebirds usually lay 4 to 5 light blue eggs, but may lay as many as 6 or 7. A small percentage of their eggs may be white. The incubation period for bluebird eggs is 12 to 14 days. Nestlings remain in the nest 18 to 21 days before they fledge. Remove bluebird nests and those of other birds as soon as the young birds have fledged.