Unwanted Tenants. Don't let your birdhouses become homes for Starlings or House Sparrows! These birds were introduced into the contiguous United States from Europe during the mids and early 1900s. Both species spread throughout North America and have become serious agricultural and urban pests. In addition, both species compete with native North American birds for cavity_nest sites and thus may harm native bird populations. For example, nest site competition by Starlings and House Sparrows has been blamed, in part, for the population declines of the Eastern Bluebird, a cavity_nesting bird.
While it is okay to paint the outside of a bird house, do not paint the interior surfaces or the inner rim of the entrance hole. Furthermore, use only environmentally safe paints, stains or varnishes on the outside and avoid any lead_based paints that can poison birds from fumes or ingestion. Choose a bird house design with the proper interior dimensions for the desired residents: Too small of a house may cause growing birds to smother, while too large of a house will not be attractive to nesting parents. Smaller birds could also become too chilled in a larger house if they are not huddled together when needed.