The Eastern Bluebird, along with its Western and Mountain cousins, is a beloved native songbird that relies on tree cavities for nesting. Because natural cavities are often scarce, providing a properly constructed and placed nest box is a direct and effective way to support their populations. Success in attracting and safely fledging young bluebirds depends not just on the box design, but on the precise setup and maintenance of the nesting site. This guidance focuses on the practical steps needed to create an optimal and secure home for these cavity-nesting species.
Determining the Optimal Mounting Height
The ideal vertical placement for a bluebird house is generally between four and seven feet from the ground to the bottom of the box. This height range balances the bluebirds’ preferences with the necessity of deterring terrestrial predators and ensuring easy human access for monitoring.
Mounting the box at least four feet high helps to discourage common ground predators like raccoons and stray cats, which are less likely to attempt a climb on a smooth pole. This distance also makes it more difficult for them to reach up and into the entrance hole. Conversely, keeping the box below seven feet allows the “bluebird landlord” to safely open the access door for regular monitoring and cleaning without needing a tall ladder.
The North American Bluebird Society often recommends mounting the entrance hole at least five feet above the ground for added security against climbing animals. While bluebirds may use boxes mounted as high as 15 feet, the lower, more manageable height is preferred because it facilitates the weekly nest checks.
Selecting the Best Location and Habitat
The surrounding environment is important, as bluebirds seek open, grassy areas where they can easily spot and catch insects. Preferred habitat includes open fields, pastures, golf courses, or large lawns with scattered trees used as perching spots. The nest box should be placed at the edge of this open space, typically 25 to 100 feet from a nearby tree or shrub, which offers a safe landing area for young birds on their first flight.
The best practice is to mount the nest box on a smooth, freestanding metal pole, such as electrical conduit, rather than directly on a tree or wooden fence post. Mounting on wood provides easy access for climbing predators like raccoons and snakes. Positioning the entrance hole should be done to avoid the most intense afternoon sun and prevailing winds, often meaning a northeast or southeast facing direction.
If placing multiple boxes, they must be spaced appropriately to account for the bluebirds’ territorial nature. Eastern and Western Bluebird nest boxes should be separated by a minimum distance of 100 yards to prevent conflicts between nesting pairs. However, two boxes can be placed in a pair, about 5 to 25 feet apart, to encourage a bluebird to use one and a non-competing species, like a Tree Swallow, to use the other.
Ensuring Safety with Predator Guards
Proper height alone is insufficient to protect a bluebird nest from determined predators, making the use of a pole baffle a mandatory companion to the mounting setup. Raccoons, snakes, and even flying squirrels are adept climbers that can easily scale an unguarded pole to access the box contents. A well-designed baffle prevents these animals from reaching the nest box.
The most effective devices are conical or stovepipe baffles, which are metal cylinders or cones installed on the mounting pole below the box. A stovepipe baffle should be at least 24 inches long and 8 inches in diameter, mounted high enough so that its bottom is at least four feet above the ground. These designs create a physical barrier that climbing animals cannot navigate, ensuring the pole remains slick and difficult to grasp.
A second type of protection involves attaching a metal plate or a specialized wooden block, known as a Noel guard, around the entrance hole of the box itself. This guard extends the tunnel depth, making it impossible for a raccoon or cat to reach inside and extract the eggs or nestlings. Combining a pole baffle to stop climbing with an entrance guard to prevent reaching offers the most comprehensive defense against common threats.
Essential Annual Maintenance
Long-term success requires regular stewardship, including cleaning the nest box after each brood has successfully fledged. Bluebirds often raise two or three broods in a season, and removing the old nest material encourages them to begin a new nest quickly. Old nests can harbor parasites, such as blowfly larvae, which can harm the next generation of nestlings if left in place.
The deep cleaning should occur at the end of the nesting season, typically in late summer or early fall after the last young have departed. Use a putty knife or stiff brush to scrape out all debris and nesting material, and discard it far away from the box, as the scent can attract predators. While a mild bleach solution can be used to sanitize the interior, ensure the box is thoroughly rinsed and completely air-dried before closing it again.
In late winter or early spring, before the new nesting season begins, inspect the box and pole for any structural damage or necessary repairs. Check that the entrance hole has not been enlarged by squirrels, which can be fixed by applying a metal hole guard, and confirm the predator baffle is still securely mounted. Maintaining the box in this way provides a safe, clean, and immediately available cavity for the returning bluebirds.