Eastern Bluebirds are secondary cavity nesters, relying on existing holes rather than excavating their own. The decline of natural nesting sites has made human-provided nest boxes crucial for conservation. Attracting these songbirds requires attention to precise specifications for the structure and its surrounding habitat. This involves creating a safe nesting environment that mimics natural preferences while mitigating threats from predators and competitors.
House Design and Installation Requirements
The physical structure must adhere to specific dimensions to ensure bluebird occupancy and safety from aggressive species. Untreated wood (cedar, cypress, or pine) at least three-quarters of an inch thick is the preferred material, offering insulation and mimicking a natural cavity. The interior surface of the front wall, beneath the entrance, should be roughened or scored to provide a grip for fledglings to climb out easily.
A precise entrance hole diameter is the primary defense against non-native competitors like the European Starling. For Eastern Bluebirds, the hole must be cut exactly 1 1/2 inches in diameter; a larger opening risks starling entry, while a smaller one may deter the bluebirds. The box should never include an exterior perch. Bluebirds do not need one for landing, but a perch provides leverage for House Sparrows and other predators.
Ventilation and drainage are fundamental to nestling health. Small gaps or drilled holes near the top of the side panels provide air circulation to prevent overheating during hot summer months. The floor of the box requires drainage holes, typically one-quarter inch in diameter, to allow rainwater to escape, keeping the nest dry and sanitary.
Proper mounting is significant for security and bluebird preference. Nest boxes must be mounted on smooth, round metal poles, such as galvanized electrical conduit, rather than on wooden posts or trees. Climbing predators like raccoons and snakes easily scale rough surfaces. A slick metal pole, minimum one-half inch in diameter, provides a reliable barrier. This ensures the nest box is a free-standing structure preferred by bluebirds for a clear flight path.
Strategic Location and Environment
The choice of location is the greatest factor in successful bluebird attraction. Bluebirds favor open country habitats like pastures, golf courses, large lawns, and orchards where short grass allows them to spot insect prey easily. Placing a box in a dense forest or near heavy brush is counterproductive, as these areas attract native competitors, particularly House Wrens, which can destroy bluebird nests.
The ideal mounting height places the bottom of the box approximately five feet above the ground, which is convenient for monitoring and discourages ground-level predators. The entrance hole should generally face east or southeast to shield the nest from harsh afternoon sun and heavy prevailing winds. The front of the box must face an open area where the bluebirds have a clear view of their foraging territory.
Multiple nest boxes must be spaced appropriately to minimize territorial disputes. Eastern Bluebirds are highly territorial and require a minimum distance of 100 to 150 yards between boxes to prevent males from driving away neighbors. Installing a nest box in late winter or early spring (typically by mid-March) ensures it is available when bluebirds begin scouting for nesting sites.
An exception to the spacing rule is pairing boxes, placing a second box 5 to 20 feet away from the first. This strategy allows bluebirds to occupy one box while a different native cavity-nester, such as a Tree Swallow, occupies the second. Bluebirds tolerate other species close by, and this method maximizes the usage of suitable habitat while respecting the territorial needs of the bluebird pair.
Deterring Predators and Competitors
Protection from climbing threats is mandatory and is accomplished using a properly installed predator baffle on the mounting pole. A stovepipe or cone baffle, made of sheet metal and at least six to eight inches wide, must be secured to the pole below the box. This device should be positioned so the top edge is at least four feet off the ground, preventing raccoons, snakes, and squirrels from accessing the nest.
Managing non-native competitors, especially the aggressive House Sparrow, requires active intervention. House Sparrows are drawn to areas with human habitation and accessible food sources. Locating a bluebird house at least 100 feet away from buildings, barns, and bird feeders that offer cheap grains helps reduce their presence. Regular monitoring is necessary to promptly remove any House Sparrow nesting material, which is typically a messy accumulation of grasses, trash, and feathers.
Once a bluebird pair is actively nesting, a temporary visual deterrent known as a “sparrow spooker” can be installed above the box. This device features fluttering strips of mylar or plastic that deter House Sparrows, which are wary of movement, but do not bother the nesting bluebirds. Placing the spooker only after the female bluebird has laid her first egg ensures the new contraption does not cause the bluebirds to abandon the site.