The top can be lifted for viewing without disturbing the nestling and easy monitoring of the nest-(it is not recommended to open the box day 13 or after as this may cause fledglings to leave the nest too early). The side is easily opened at the end of the nest season for cleaning. It is important to clean out old nesting material that may harbor parasites.
Mounting Bluebird Boxes
If Tree Swallows compete for the nest site, place another box near the first (15 to 25 feet from the original house). They seem to tolerate overlapping territories of other species, but bluebirds will not nest less than 300 feet from each other. Both swallows and bluebirds are dependent on cavities for nesting, but otherwise they are different in many of their survival strategies. Bluebirds feed on ground-dwelling insects while swallows feed on insects in the air. Given places to nest, they can coexist within an area quite effectively. It may even be beneficial for bluebirds to have swallows nearby to warn them of potential predators or danger.
One important item to mention is that sparrows may try to take over a bluebird nesting box. They may find the box first or they may try to force the bluebirds out. The only way to help reduce this possibility is to make sure the house is mounted away from the edge of trees or away from human dwellings and to remove the nests before they are complete (a sparrow nest is a sloppy collection of grasses or litter that fills the box). You can also leave the top and side of the nestbox open to make it less desirable until the sparrow relinquishes its claim on that house.