The Western Bluebird Nesting Preferences
Bluebirds normally maintain a territory for the purpose of mating, nesting and feeding. Territories are directed toward a round area. In Arizona, the average size of their territory is reported at 0.4 hectares. These birds have also a keen vision enabling them to monitor potential predators. If they feel threatened, they fly away and seek protection in trees or shrubs nearby.
The western bluebird likes to build its nest in open areas like farms, forests and grasslands with enough trees and shrub cover. They also occupy open fields with several big oak trees, pastures, vineyards, old orchards or huge mowed yards with some medium-sized trees. Their preferred trees include oaks, blue, Engelmann or coast live oak or conifers, coulter and bishop pine, sycamores, cottonwoods, ashes. Other ideal habitats for them are forest openings and clearings and agricultural areas. During winter, these birds inhabit open and semi-open terrain notably pinon-juniper forests, farmlands and deserts.
Western bluebirds are cavity nesters. Where there are available nesting sites, their population increases. They prefer to nest in natural sites such as holes in trees or buildings, old tree holes previously occupied by woodpeckers and man-made nest boxes. The nest cavity, about two to five meters high above the ground, provides shelter to both adults and their young especially during the breeding season. The western bluebird, however, is often forced to leave their many nesting sites by the European starling much like the eastern bluebird. The European starling is a very aggressive bird capable of pushing baby birds of other species out of their nest and claiming the nest.
Bluebirds are very responsible parents. The male takes charge in establishing and protecting their nesting territory usually by singing while the female constructs the nest shaped like a cup and made mostly of dry grass as well as twigs, weeds and finer plants materials for the inner lining. The male may sometimes help in the nest building process. During the breeding season, she lays from four to six eggs on the nest and incubates them alone for up to 14 days until the eggs hatch. Although both parents feed the nestlings during their first three weeks in the nest, it is the female that continues to brood the young.
After fledging, both parents still feed their offspring for two to three weeks until they know how to fend for themselves. However, the male assumes most of the responsibility as the female is already occupied in adding more materials to the nest and laying four to five more eggs for her second clutch.