Bluebirds, including the Eastern, Western, and Mountain species, are well-loved songbirds known for their vibrant plumage and melodic calls. Understanding their nesting preferences and the specific locations they choose is key to appreciating these birds. Their nesting habits reveal much about their adaptability and reliance on environmental conditions.
Preferred Natural Habitats
Bluebirds are secondary cavity nesters, utilizing existing holes for their nests rather than excavating their own. They seek out old woodpecker holes in dead trees, hollows formed by decay, or openings in broken limbs. These natural cavities are found in trees like pine, oak, aspen, and cottonwood, often up to 50 feet above ground. Bluebirds also use cavities in fence posts or utility poles.
Their preferred natural environments are open country with scattered trees and minimal undergrowth. These include open woodlands, pastures, orchards, and clearings. They thrive in semi-open habitats such as farmlands, roadsides, and suburban parks and backyards with extensive lawns and suitable nest sites. These open grassy areas are important for foraging, allowing bluebirds to spot insects from perches on trees or fence posts before swooping down to catch prey.
Structure and Materials of Their Nests
Once a suitable cavity is selected, the female bluebird constructs the nest. She weaves materials to form a cup-shaped structure. The primary components are fine grasses and pine needles.
The nest is lined with softer materials such as finer grasses, animal hair, or feathers. This creates a soft, insulated bed for the eggs and young. The nest is placed near the bottom of the chosen cavity, providing a secure and protected environment. Unlike some birds, bluebird nests are clean, lacking items like seed heads or strings.
Importance of Nest Boxes
Human-provided nest boxes have become an important nesting option for bluebirds due to the decline in natural cavities. These boxes mimic natural tree hollows, offering a safe space for nesting. Standard bluebird nest boxes feature specific design elements to deter larger species like European Starlings.
The entrance hole size is important: Eastern Bluebirds use a 1.5-inch diameter hole, while Western and Mountain Bluebirds use a 1 9/16-inch hole. This size allows bluebirds entry but excludes larger competitors. Nest boxes also incorporate ventilation holes, drainage holes, and a roof for weather protection. Interior depth ranges from 4.5 to 6 inches, with a floor size between 4×4 and 5.5×5.5 inches. Nest boxes are placed in open areas, away from dense brush and heavy human traffic, on free-standing poles with predator guards to protect the contents.