Location

• Select an open location for your purple martin house. Purple martin experts recommend no closer than 40 to 60 feet to trees taller than the birdhouse and no closer than 30 to 120 feet from manmade structures. Purple martins prefer to be high in the air. The apartment-building style house should be raised 10 to 20 feet above the ground on a free-standing pole. The house should be designed to raise and lower along the pole for easy cleaning and checking of nests.
  
  

Dimensions

• Build compartments a practical size. Purple martins are large members of the swallow family, measuring 7.5 inches from head to tail. A nest box too small for them to move around easily will be ignored by the martins. Purple martin house-building experts recommend nest compartments between 6 and 7 inches wide, 9 to 12 inches deep, and 5 to 7 inches high. A common number of compartments for a complete purple martin house is 16, but colony housing to hold 32 nests is possible.
  
  The size of entry holes into the individual compartments is crucial not only for attracting purple martins, but also for curbing takeover by competing species such as starlings or predation by crows and owls. Half-circle or crescent-shaped holes 3 inches wide at the base and 1 3/16 inches tall in the center will exclude starlings, especially if located flush with the floor of the compartment. If a round hole is desired, 2 1/8 inches diameter is recommended.
  
  

Protection from Pests and Predators

• Placing purple martin houses on freestanding poles mimics their natural nesting habitat of abandoned woodpecker cavities in tall snags. This affords the nestlings some protection, but predators can still find the nests. Install pole guards to deter climbing predators such as squirrels, raccoons and snakes---a downward-facing cone works best. Purple martin houses may need to be guarded from above as well, from hawks, crows and owls. Spurs placed on the house corners will prevent these larger birds from landing.
  
  Regular checking of your purple martin house to remove unwanted occupants, such as English house sparrows and starlings, will increase the survival rate of your purple martin colony. Experts recommend trapping non-native sparrows and starlings and offering alternate housing to native bluebirds, tree swallows and flycatchers. Once purple martins have been pushed out of an apartment house by other birds, they may not consider it a housing option in future seasons. Regular cleaning of the nest boxes will reduce the incidence of parasites.
  
  Purple martins begin nesting in North America by the end of June. They spend 26 to 32 days raising their young to fledgling size. Fledglings will remain near their parents for an additional two weeks before seeking nest sites of their own for the following year. Once purple martins have abandoned the nest boxes to migrate, "landlords" should clean out the purple martin house. Store the purple martin house in a shed or garage in the fall when the birds leave to avoid hornets or unwanted bird species from taking up residence.