Once martins establish nesting colonies, they return year after year to breed. Competition from other species greatly discourages martins from taking up residency. Discourage non-native competitors such as the house sparrow or European starling by trapping or shooting them and lowering the house for tearing out nests. Nest compartments for martins should be at least six inches square, but larger compartments are preferred. Housing should be placed on some type of pole that allows nesting progress to be checked and facilitates the removal of the house during winter.
Predation is the most common reason for nest-site abandonment.
The black rat snake is incredibly adept at climbing. Use cone or wire mesh predator guards. Contrary to popular belief, recent food habit studies done on purple martins revealed very few mosquitoes in their diet. They prefer to feed on larger winged insects such as flies, wasps, beetles, and dragonflies.