With dexterous paws, they can even figure out how to undo latches to get at a meal of eggs or young birds. Raccoon attacks increase through the breeding season, affecting second and third nests most. Extra depth in the nest box should place nest contents beyond 'coons' grasp. Cats are also a serious and cunning predator of bluebirds. Nest boxes should be placed at least 100 yards from buildings, to avoid both marauding cats and house sparrows.
House wrens compete for nest sites with bluebirds.
They will fill boxes with twigs over bluebird nests. More importantly, wrens peck or throw out bluebird eggs in an effort to drive the bluebirds away. Place bluebird boxes in the open , facing away from brush to reduce this lethal competition. Starlings and house sparrows are cavity nesting birds imported from Europe during the late 1800s. Since they are more common near buildings, keep bluebird boxes at least 100 yards away.