Managing a martin colony requires that “landlords” reserve nest compartments for martins only. Starlings and House Sparrows do try to nest in martin boxes and gourds, and they should be evicted.
Housing must meet certain specifications to ensure successful nesting: housing that is 15 to 20 feet high, at least 30 feet from human housing, no tall trees within 40 feet, and entry holes of exact dimensions (3 inches wide by 1 3/16 inches high).
Making the houses accessible – which means being able to reach the housing -- is a major advantage for monitoring and managing a colony. Purple Martins appreciate human activity in the vicinity of their nests, not only because they are sociable birds, but also because humans and their pets help protect martins from predators. Predators include owls, hawks, snakes, raccoons and squirrels.