Bluebirds do not build nests the same way that other species, such as robins or doves, construct them. Bluebirds need a cavity, such as a woodpecker hole or a hollow limb, which provides walls that help hold their nesting materials together. That’s why bluebird nesting boxes, or bluebird houses, are treasured by the birds. Bluebirds prefer a clean house where they can bring in fresh nesting material. Clean the nest not long after young birds leave, when invasive species rather than bluebirds build and immediately after birds fledge should you suspect a parasitic attack.
When Young Birds Fledge
Keep a close watch on the nesting box once the female bluebird has laid a clutch of eggs. You can even open the box as a way of monitoring progress. Be careful as you swing the door open, so as not to drop any eggs or damage the hatchlings. Don't worry about leaving human scent behind. Most birds, including bluebirds, do not have a keen sense of smell. Once you know that the last fledgling has left the nest, it’s time to clean the box and get it ready for the next brood. Cleaning the box after the last fledging leaves encourages bluebirds to return during the breeding season. These birds build nests and raise young up to three times each season. At a minimum, clean the box in February, before bluebirds arrive, or in September, after the last fledglings of the final brood depart.
Keeping an eye on the nesting box and checking the inside periodically when young birds are on the nest also protects against invasive species. House sparrows are an example of invaders that attack bluebirds, take over the nest, and even build on top of the birds they kill. House sparrows are aggressive and may chase bluebirds away from a nesting box before the bluebird even has a chance to build. Clean the box of nesting material if house sparrows build inside. House sparrows build nests from grasses, weeds, feathers, hair and litter they find in the yard, and they lay brown and white speckled eggs. Bluebirds use finer grass blades, pine needles, thin roots and, sometimes, deer hair. Their nests tend to be neater and more symmetrical than those of house sparrows. House sparrows are not protected by migratory bird legislation.
Besides chasing away invasive species, cleaning bluebird houses also prevents infestations from parasites. Mites, ants and other small insects can invade a bluebird house, but the species is especially prone to attack by blowflies. The female blowfly lays eggs in the nesting material. When they hatch, they suck the blood of young birds. The insects then drop back into the nesting material to pupate and emerge as adult blowflies. Nest box cleaning rids the the bluebird house of these potentially harmful parasites and pests. Bluebirds sometimes build a layer of material on top of an existing nest. Cleaning avoids parasitic attack and prevents the nest top from being too close to the opening, where young birds are more accessible to predator attacks.
Box Cleaning Process
You can clean a bluebird house by scraping out the old nesting material with a screwdriver or putty knife. Using a few extra precautions is optional. For example, wear a dust mask to prevent exposure to airborne particles and avian diseases. Seal the nesting material in a plastic bag before putting it in the trash to avoid attracting predators. Wash the house by spraying the inside with water from a garden hose in order to remove the last bits of debris. Leave the house open for several hours so that it can dry.