Food: Eastern bluebirds consume 70 percent animal matter and 30 percent vegetable matter. Vegetable intake increases to more than 50 percent in December and January, but is completely lacking in May. Animal matter includes grasshoppers, crickets and katydids, various coleoptera, moths and caterpillars, some hymenoptera and hemiptera, as well as various other invertebrates and small vertebrates. Vegetable matter is mostly wild fruits (Bent 1949).
Western bluebird
Sialia mexicana
L 5½″
Habitat: The western bluebird is most abundant in open ponderosa pine forests of the Transition Zone, but may also be found in oak woodlands, pinyon-juniper, mixed conifer, and subalpine forests.
Nest: Nests are usually in old woodpecker holes, but this bird also uses natural cavities. Nests have been reported in oak, sycamore, and pine trees. In Monterey County, California, nests were found from 5 to 40 feet above ground in pine stumps or trees (Bent 1949). This bluebird, like the eastern, also readily nests near humans in bird houses. Nest boxes should be 5 × 5 × 8 inches with a 1.5-inch entrance hole located 6 inches from the floor. Boxes should be placed 5 to 10 feet above ground near forest openings or meadows.
Food: Beal (Bent 1949) examined the contents of 217 stomachs and found 72 percent animal material (grasshoppers 21 percent, caterpillars 20 percent, useful beetles 9 percent, other beetles 16 percent, ants 5 percent, other hymenoptera 1 percent) and 28 percent vegetable material, mostly wild fruits, including elderberries, mistletoe berries, blackberries or raspberries, prunes, cherries, and a few weed seeds.
Mountain bluebird
Sialia currucoides