Not all blue birds are bluebirds; for instance, the California Scrub Jay is blue but its a corvid, more related to crows. Bluebirds belong to the thrush family.
Open woodland- perched on low branches, post, and/or fences, common the Los Angeles year round but also more abundant in winter months.
In cavities- either naturally occurring, man made or made by other birds, they don't have the bills to carve out their own.
Omnivore- primarily insects in the summer, and fruit and seeds in the winter, occasionally snails and worms.