The Western Bluebird, like the Eastern Bluebird, is a cavity nester. In short, they need old woodpecker holes to nest. Unfortunately the introduced English Sparrow also uses old woodpecker nests, and is more aggressive than the Western Bluebird. Luckily Western Bluebirds readily accept man-made nest boxes. If you live in an area with Western Bluebirds build a few dozen boxes for these beautiful native birds, then keep the English Sparrows at bay!