Last week I saw an enormous flock of purple martins staging west of Apalachicola before continuing their migration. The birds roosted shoulder to shoulder on two strands of power wire stretching over a quarter mile.

Earlier in the week, I watched a martin house at Harry and Linda Arnold’s riverside and Harry told me the last of the chicks were fledging which triggers the migration each year. The Arnolds have several successful martin houses on their deck and said the martins keep the yard free of mosquitoes.

The purple martin (Progne subis) is the largest swallow in North America. Males are all dark, glossy blue-black; females are duller above and grayish below. They have a distinctly notched tail and, like all swallows, are graceful agile flyers.

The genus name of the purple martin, Progne, is from the Greek word Prokne, the daughter of Pandion, a king of Athens. Legend has it she was changed into a swallow to escape her brutal husband. The species name, subis, given by the Roman naturalist Pliny, is Latin for "a bird that breaks eagle's eggs." Other names for the purple martin are the gourd martin, western martin, house martin, and black martin.

So popular are these birds, there is a conservation group devoted specifically to them, the Purple Martin Conservation Association (PMCA), a 501(c)3 nonprofit organization.

Often, purple martin houses fail to attract a colony. There are several reasons why this might happen.

A martin house must be placed in a large open area more than 30 feet from human housing. They prefer to nest close to water. There should be no trees within 40 feet.

Martin houses should be 15 to 20 feet off the ground. Commercially built houses and a variety of plans for houses are available.

White housing attracts martins best, and reflects sunlight, keeping nests cooler. Compartment floor dimensions should be at least 6" x 6," but larger compartments offer better protection from predators and rain.

You can improve a martin house by adding insulation to the attic and remodel interiors to offer double-size compartments. Dividers between compartments help keep males from claiming extra space, and can double occupancy rates. They also keep nestlings from wandering to other compartments, where they can get lost and die, or steal food from younger nestlings.

All birdhouse poles require climbing animal barriers to keep out snakes, squirrels and raccoons. You can install guards before or after your martins have arrived. In areas with fire ants, Teflon spray or a ring of grease on the pole will stop the ants.

Adult martins return to the sites where they nested before. Year old martins breeding for the first time typically colonize new sites, and begin arriving about four weeks after the first adults. Keep a new martin house closed until about a month after you see the first martin scouts in your yard. This will keep house sparrows and starlings from taking over.

The PMCA wants help in collecting information on martin arrival dates and breeding success. They have two programs to collect this data, Martin Colony Registration and Project Martinwatch. Information on these programs and martins in general is available at