Anatomy of Purple Martin housing
Multi-compartment House: A single pair will nest inside each individual compartment. Houses are available in a variety of styles, sizes, and materials.
Gourd: Martins build nests inside man-made and natural gourds. Modifications provide compartment access to both martins and humans.
Entrance Hole: Provides access to the compartments. Entrance holes are available in round and several different starling-resistant shapes and are often accompanied by a porch.
Perch Rods: Provides a place for the martins to rest while they preen their feathers, watch for predators, and survey the colony site.
Owl/Hawk Guard: Vertical rods placed across the front of the house or gourd to prevent owls and hawks from reaching into the cavities.
Pole: Elevates the housing compartments and allows for easy raising and lowering. Poles function on a telescoping, rope & pulley, or winch (shown) system.
Predator Guard: Keeps predators like raccoons and snakes from climbing the pole.
Vertical Accessibility: Martin housing should raise and lower vertically on a telescoping, pulley, or winch system. Housing will need to be lowered, sometimes on a daily basis, to remove competitor nests and to monitor the nests.
Height and Installation of Pole: Recommended height is 12-18’. Poles should be securely set in concrete with 18”-25” below ground. Many manufacturers offer mounting sockets or stakes so that landlords can relocate or remove their poles.
Material: Aluminum, thick plastic, wood, and natural gourds are all suitable materials for martin housing, provided that the exterior of the house is white in color. White reflects heat, keeping housing cooler in hot temperatures. Wooden housing should be made from untreated material only. Wood 3/4” thick will provide better insulation against heat and cold. Cedar, cypress, or redwood works well. Plastic houses and gourds should be of thick (preferably UV-resistant) material and should not allow light to filter through the walls. Transparency creates a “greenhouse effect” increasing the temperature which can be deadly for nestlings. A layer of insulation in the attic of plastic or metal housing will protect martins during periods of extreme temperatures.
Entrance Hole: Traditional round entrance holes are generally 2-1/8” in diameter, but a range between 1-3/4” and 2-1/4” is acceptable. Round entrances should be placed 1” to 1-1/2” above the floor or porch. Starling-resistant entrance holes (1-3/16” tall x 2-3/4” to 3” wide) should be placed so the bottom of the entrance is flush with the compartment floor, or not more than 1/4” above it. With gourds a porch is not required with a starling-resistant entrance although many landlords use them.
Compartment Interior: The minimum size for compartments is 6” x 6”, but research has shown that larger compartments (measuring 7” x 12”) offer greater protection from predators and the elements, and will keep nestlings more comfortable. Gourds should be no less than 8” in diameter, with gourds in the 10-12” range being ideal. Adult martins are 7.5” long, so compartments must be large enough to accommodate 4-6 nearly-grown nestlings and both parents. Houses with smaller rooms can be remodeled to offer larger two-room suites. Nestlings are less likely to jump prematurely when they are kept comfortable and cool inside the house. Wooden houses and natural gourds should have a natural (unpainted) interior. Metal or plastic housing with flat, slick floors could result in young developing permanently splayed legs—a potentially fatal abnormality that can be prevented by providing textured subfloors in each compartment.
Weather Protection: Martin houses should be placed in an open area and therefore will be fully exposed to wind, rain, and summer sun. Good ventilation, drainage, and insulation are important features for successful nesting. Nestlings under 10 days old are unfeathered and prone to hypothermia, so it is important that they do not become chilled in a rain-soaked nest. Ventilation holes should be drilled at an upward angle or placed under the roof overhang to prevent water from funneling into the compartments. Drain holes in the bottom of each compartment or gourd will allow wet nests to dry more quickly. The roof overhang can be extended to help protect compartments from rain, and raised subfloors also offer protection. A layer of insulation in the attic of plastic or metal housing will protect martins during periods of extreme temperatures.