Don't let the old nesting material build up too high, however, because the nest becomes too close to the entrance hole, making the young vulnerable to predation. Bluebird families tend to stay together for the summer, and by early August they form flocks with other family groups near the nesting area. Both juveniles and adults undergo a molt in later summer and early fall, with the juvenile birds molting into their adult plumage. In September and early October, they depart for their wintering grounds in the southern states and northern Mexico. Setting up a Bluebird Trail Nestbox Placement Bluebirds hunt for their food on the ground, so boxes should be placed in pastured areas or mowed lawns where insects can be seen.
Ideal habitat is an open, closely-cropped area bordered by trees and shrubs.
Nearby trees and bushes provide the birds with perching sites which are used for a variety of activities, including looking for intruders and predators, and interactions with their mate. Treed areas also provide important cover for the young when they fledge. Areas adjacent to cereal crops are less desirable for nestbox trails because it is difficult for the birds to locate their preyon the ground and because of the risk of pesticides being sprayed in the area. Nestboxes should not be placed around farm buildings because of the competition and potential disturbance by House Sparrows. Boxes placed in or close to treed or brushy areas will be dominated by House Wrens, which will often destroy bluebird eggs and young.