ANR-612, Reprinted December 1996. By Lee Stribling, Extension Wildlife Scientist, Associate Professor, Zoology and Wildlife Science, Auburn University.

Attracting Purple Martins

The purple martin is a welcome warm-weather guest of suburban and rural backyards throughout Alabama. Its late winter arrival on the Gulf Coast signals the withdrawal of winter and heralds the return of spring.

Choctaw and Chickasaw Indians first noticed the tendency of purple martins to nest in man-made structures and provided hollowed-out gourds to attract them. European settlers followed suit. More elaborate bird houses have since been developed, but gourds still remain popular and attractive to martins.

Physical Characteristics

Purple martins are fast fliers, capable of strong, extended flights. Like most other swallows, they feed almost totally in flight and can sail with little effort while feeding.

When in flight, adult male purple martins appear jet black. Closer observation reveals dark purple-blue feathering over most of the body. In contrast, females appear much duller with only traces of blue evident. Their chin, breast, and abdominal plumage appears pale gray to white.

The process of replacing old feathers with new ones is called molting. Until martins complete their second fall molt, young males are hard to tell from females. Dull blue feathering is easy to see on their heads and backs, but patches of gray and white remain over much of their bodies. Although sexually mature by 12 months of age, full adult status is not achieved until the birds molt into dark blue plumage when 15 to 17 months old. Adult martins measure about 7 inches in length.

Life History

Purple martins avoid harsh winter weather by migrating each fall to South America. Brazil harbors the largest wintering concentration. Literally millions of martins are found there during fall and winter months.

Their annual journey to breeding grounds in North America usually begins, varying somewhat with weather patterns, curing January. Early arrivals, typically adult males, may reach the Gulf Coast as early as late January. Female and sub-adult, or first year, martins soon follow. Their inland migration to nesting sites, once reaching the North American coast, may extend into May.

Many purple martins return to the same nesting area they used previously. In fact, some will even nest in the same room of the birdhouse they used the preceding year.

Adult martins generally begin nest construction during late March and early April. Sub-adult martins may delay nesting until late April or early May. Nests are constructed of stems, leaves, and mud. Once complete, three to eight (most often four to five) off-white eggs are laid. Incubation lasts about 14 days and is performed solely by females. If the first nesting attempts fail, purple martins will re-nest. Nesting efforts are usually complete by early June.

Both sexes share parental care of young martins and may feed them hundreds of insects each day until the young birds leave the nest or fledge. Young usually remain in the nest for 3 to 4 weeks before fledging. They sometimes return with their parents to the nest cavity during the first few nights after fledging, but become entirely independent soon thereafter.

Most purple martins, except a few late nesters, leave their nesting areas before August. By October, almost all have migrated across the Gulf of Mexico to wintering grounds in South America.

Housing For Purple Martins

Historically, purple martins nested in cavities they found in dead or dying trees in open woodlands and cutover forests. Most western populations still depend heavily on natural cavities, but eastern populations have adapted readily to nesting in man-made structures. Two basic types of man-made nesting structures are attractive to purple martins.

Gourds. Hollowed-out gourds are the simplest, least costly method of providing nest sites for purple martins, but require periodic replacement.

1. Select dried gourds measuring at least 8 inches in diameter and 6 inches tall for nesting cavities (martins prefer larger sizes).

2. Lightly sand any black mold off the outside of the gourd.

3. Cut or bore a circular 2-1/4-inch entrance 3 to 5 inches above the inside floor.

4. Remove all pith and seeds.

5. Optional: Paint or varnish the outside of the gourd. Use light-colored paint to reduce heat accumulation inside the cavity.

6. Bore four or more 1/4-inch holes in bottom of gourd to allow water to drain out.

7. Bore four or more 1/4-inch holes around the neck of the gourd, 3 inches from its top to provide increased ventilation.

8. Erect six to eight gourds, suspended from a horizontal bar attached to a pole (preferably galvanized pipe to discourage predation by climbing animals), about 8 to 15 feet above the ground.

Martin houses. Martin houses are usually the most secure man-made nest sites. In addition, they require considerably less space than gourds do. Many different designs of nest structures are used by mar tins, but some general specifications apply to all.

1. Entrances should measure at least 2 inches in diameter, but not exceed 2-1/2 inches.

2. More than one entrance, placed preferably on different sides of the birdhouse, should be provided for each compartment.

3. Floor space should measure at least 6 inches by 6 inches, with a minimum ceiling height of 4 inches.

4. Wide porches, at least as wide as entrance holes, should be provided.

Maintenance. Regardless of the type of nesting structure used, most structures, with even minimal maintenance, remain attractive to purple martins for years. Nesting boxes and gourds should be removed and stored, or the entrances plugged, each year after martins leave. This practice will discourage starlings, sparrows, and other nuisance birds from taking over nest boxes.

During winter inspection or storage, remove old nest materials and check for wear or structural defects. Unplug or erect nest structures immediately prior to the anticipated return of migrating purple martins.