Western Bluebird

Western Bluebird

The western bluebird, Sialia mexicana, is dependent upon savanna and grassland habitats that require periodic fire for maintenance. Preferred habitat is open grassland, farm or range land with sufficient tree and shrub cover for nesting and perching. Western bluebirds also occupy oak woodland, pine parkland, and cleared areas within forest stands and transition zone forests. Like all secondary cavity nesting birds, bluebird populations are limited by the availability of suitable nesting sites. Holes in trees, frequently dead snags excavated by woodpeckers, are preferred natural nesting sites. Nest cavity heights vary from 2 - 5m above ground level. The nest cavity provides both adults and young with cover during the breeding season. Bluebirds will readily use nest boxes in areas devoid of natural cavities but where other habitat components are present.

The western bluebird is predominately an insectivore. Bent (1949) described the bluebird's diet as 92% animal and 8% vegetable. Typical insects in the diet include grasshoppers, beetles, ants, wasps, flies, and caterpillars. Vegetable items include small fruits such as currants, grapes, elderberries, and mistletoe.

Bluebirds maintain a territory used for mating, nesting, and feeding. Territories tend toward a round or elliptical configuration. Mean territory size for western bluebirds in Arizona is reported as 0.4ha. Bluebirds utilize a keen sense of vision to detect potential threats, and if threatened, take flight and seek protection in nearby trees or shrubs (Balda, 1967, 1975).

As seen in figures 70 and 71, Bluebird habitat could expand by about 85,000ha in Plans Build-Out, largely because of the increased openness of new rural residential areas. However, these habitat changes are made less attractive because of the parasitic role of cowbirds in the same areas, and increased fire suppression associated with rural residential development.