Purple martins are the largest swallow in North America. They hunt and drink water in flight, flying low over lakes and ponds with open bills scooping drinks. It makes sense, then, that the birds enjoy a habitat of open areas with nearby water. The bird often nests in man-made birdhouses. Gourds are a popular type of nesting site that have been provided by Native Americans for purple martins since before Europeans came. Martins like to nest in colonies.
Obtain or grow gourds.
Mix a bleach solution of one part bleach and 10 parts water and wash the gourds in it. Dry them.
Store the gourds on newspaper in a warm, dry spot like an attic for three to six months, turning them frequently.
Clean the gourds often with the bleach solution, wiping off the mold that will develop. If a gourd softens or wrinkles, discard it.
Shake the gourds occasionally to see if they are cured. If seeds rattle, a gourd is ready.
Prepare the Gourds
Soak the gourds in soap and hot water for 15 minutes.
Scrape the gourds with the knife to remove the outer skin and remaining mold.
Rub the gourds thoroughly with steel wool.
Rinse the gourds and allow them to dry completely.
Make the House
Drill a 2 1/8-inch hole in the most concave part of each gourd so that the opening faces directly out---not up or down.
Drill seven holes spaced about 2 inches apart for drainage in the bottom of each gourd, using a 5/16-inch bit.
Drill four equally-spaced holes with the 5/16 bit 2 inches from the top of each gourd. Using the opening as the front, two holes should be on the gourd's front and back, with the other two holes on either side.
Scrape out the inside of the gourds with the spoon or, if this proves difficult, soak the gourds for a few hours.
Soak the gourds in wood preservative for 15 minutes.
Hang the gourds to dry for several days.
Sand the gourds until smooth.
Prime the gourds and allow them to dry.
Paint the gourds with two coats of paint, making sure not to block the holes.
Thread the wire through one set of the opposite holes drilled at the neck.
String a support line 10 to 15 feet off the ground.
Hang the gourds from the support line with entrance holes facing the most open area. Make sure gourds can only swing in one back-and-forth direction and that no gourds can swing 360 degrees.