Purple Martins spend the non-breeding season in Brazil then migrate to North America to nest.  East of the Rockies they are totally dependent on human-supplied housing. 

Most "would-be" martin landlords rush to get their martin housing opened up for the arrival of martin "scouts" in their area.  Contrary to popular folklore, "scouts" are not looking for new breeding sites for their flocks.  Scouts are simply the first martins to arrive in, or pass through an area on their way back to their previous year's nesting site.  These martins aren't likely to switch to new housing.

Landlords of active sites can leave their housing conpletely closed up until the martins return and land on the housing, usually around April 15 in our area.  Purple Martins exhibit a very high level of site fidelity.  Once they have bred successfully at a specific location, the same birds return there year after year.

Houses and gourds should be painted white, or a light pastel color; trim can be any color.  White housing reflects the heat of the sun, keeping nestlings cooler.  Compartment height can be from 5" to 7" high.  Place entrance holes about 1" above the floor.  Hole size of 2 1/8" is recommended.