The Purple Martin (Progne subis) is the largest swallow species in North America. In the eastern part of the continent, they are dependent on human-provided housing for nesting. Because these birds are highly colonial, establishing a successful colony relies on precise timing. Martins migrate thousands of miles from South America to their North American breeding sites. Having the house ready before the first arrivals is the only way to attract them, as competition for nesting cavities begins immediately.
Understanding Purple Martin Migration
Purple Martins are long-distance migrants, spending their non-breeding season in the Amazon basin of South America. Their return journey to North America is a marathon, covering up to 7,000 miles, with some birds flying over the Gulf of Mexico in a single push. The first birds to arrive back in the spring are known as “scouts,” referring to the oldest (After Second Year or ASY) adults.
These scouts are usually males returning to claim established territories and secure the best nesting spots. The younger birds, known as sub-adults (SY), are the ones most likely to start a new colony. They arrive four to twelve weeks later than the scouts.
The migratory pattern follows a distinct wave, beginning along the Gulf Coast and progressing northward and westward. Housing must be open and ready well in advance of the first anticipated scout arrival in a given latitude. The exact date can vary by up to a month each year, so preparation for the earliest possible date ensures a successful start to the nesting season.
Regional Guide to Raising Housing
The best time to raise a Purple Martin house is determined by latitude, as the birds migrate progressively north. Housing should be raised and ready at least one to two weeks before the earliest expected scout arrival date.
In the Southern States and Gulf Coast, including Florida, Louisiana, and Texas, scouts arrive early, often in January. Landlords in the Deep South should have their houses ready to open by the third or fourth week of January, with late January to mid-February being the general window for opening. For example, scouts have been reported in central Florida by the end of January.
The Central States and Mid-Atlantic region see arrivals later in the spring, typically starting in March. Areas like Kentucky can expect their first scouts around the second or third week of March. Further north, in states like Illinois, the arrival window shifts to late March through the first two weeks of April.
In the Northern States and Canada, martins are the last to arrive, following warming weather and insect emergence. Housing in these areas should be raised by the end of March to mid-April at the latest. Monitoring local birding reports, such as the Purple Martin Conservation Association’s Scout-Arrival Study, provides the most accurate, real-time data for precise timing.
Preparing the Site and Housing Structure
After identifying the correct timing, physical preparation of the nesting site is necessary for a successful colony. Martins require a large, open area with a clear flight path in all directions. The house should be placed at least 40 feet away from tall trees or buildings, which provide cover for predators.
Houses are typically placed between 12 and 20 feet above the ground. A pole that can be easily raised and lowered is necessary for management, allowing for nest checks and the removal of competitor nests. A predator guard must be installed on the pole to deter climbing animals like raccoons and snakes, which can quickly wipe out an entire colony.
Before raising the house, ensure all compartments are clean, dry, and free of old nesting material. The housing should feature proper ventilation and drainage holes. Although the house must be raised before the martins arrive, the entrance holes should remain plugged until the first scout is sighted. This prevents non-native, invasive birds from claiming the cavities.
Managing Competition and End-of-Season Care
A primary challenge for Purple Martin landlords is managing competition from non-native species, specifically the House Sparrow and the European Starling. These aggressive birds compete fiercely for nesting cavities and can injure or kill native birds and their young.
Active management is required, starting by keeping the housing entrances sealed until the first Purple Martin scout is seen. Once the entrances are opened, landlords must monitor the house daily and immediately remove any nests built by starlings or sparrows. Starling-resistant entrance holes (SREHs), which are crescent-shaped, can prevent starlings from entering the cavities while still allowing martins access.
The use of traps designed for these invasive species is an effective strategy to protect the native birds. After the breeding season is over, typically from late July through the end of August, the martins depart for their communal pre-migratory roosts and head south. Once all birds have left the colony for the winter, the house should be lowered, cleaned thoroughly, and stored or sealed. This cleaning prevents parasites from overwintering and ensures the house is ready for the next season’s arrivals.