Purple Martins are the largest swallow species in North America, valued for their aerial displays and social behavior. In the eastern part of the continent, these birds rely almost entirely on human-provided housing for nesting. Attracting a colony involves understanding their housing requirements, the ideal location and timing for installation, and the ongoing commitment to protecting them from competitors and predators.
Essential Housing Features
The design and construction of the nesting structure are fundamental to attracting a Purple Martin colony. Housing should be painted white to reflect sunlight, which helps prevent the interior compartments from overheating and causing heat stress to the nestlings. Good housing must be equipped with ventilation to manage internal temperature and drainage holes to prevent the accumulation of water inside the cavities.
Compartment size is a critical factor. Modern recommendations suggest a minimum size of 6 by 6 by 6 inches, though larger compartments, such as 6 by 12 inches, are preferred. Larger spaces allow the nest to be built farther from the entrance, offering better protection from predators like owls. Many landlords choose natural or manufactured gourds, which martins often favor due to their single-family design and the ability to customize entrance holes.
All Purple Martin housing requires a system, typically using a winch or pulley, that allows it to be raised and lowered vertically. This feature is necessary for conducting weekly nest checks, performing maintenance, and actively managing competing bird species. Entrance holes should be designed to be starling-resistant, often featuring a crescent or specialized shape, which prevents larger European Starlings from accessing the cavity while still allowing the smaller martins entry.
Optimal Placement and Seasonal Timing
Purple Martins are highly selective about the location of their colony, demanding a large, open area with a clear flight path in all directions. The housing pole should be erected at a height of 12 to 20 feet above the ground to ensure visibility and accessibility. A primary consideration is the distance from any tall trees or buildings, which should be at least 40 to 60 feet away to prevent predators from launching an attack and to maintain unobstructed flight access.
Despite their need for open space, martins exhibit a preference for nesting near human activity, with successful colonies often established within 30 to 60 feet of a residence. This proximity may stem from an evolved understanding that human presence deters natural predators from approaching the nesting site. The presence of a nearby water source, such as a lake, pond, or river, is also highly beneficial, as martins feed exclusively on flying insects and use mud for nest building.
Timing the installation is equally important, as martins are migratory birds returning from South America early in the spring. Housing should be put up in anticipation of the earliest returning scout birds, often between late February and mid-April depending on the latitude. Keeping the entrance holes plugged until the first martins arrive helps ensure that non-native competitor species do not claim the cavities before the martins have a chance to settle.
Managing Competing Species and Predators
Long-term success in hosting a Purple Martin colony relies heavily on active management of threats, particularly from non-native cavity nesters and natural predators. The two primary competing species are the House Sparrow and the European Starling. Neither is protected by law, and both will aggressively take over cavities, destroy eggs, and even kill adult martins. Passive exclusion alone is generally insufficient to deter these tenacious birds.
Active management requires weekly monitoring of the housing using the pole’s vertical lowering system to check for competitor nests. Any nests built by sparrows or starlings must be immediately removed. Landlords may use specialized traps installed within the cavities to humanely capture and manage these invasive birds.
Protection from natural predators is another management priority, which involves installing physical barriers on the pole itself. A smooth, cone-shaped or cylindrical predator guard, or baffle, must be securely placed on the pole at least four feet above the ground to prevent climbing mammals like raccoons, snakes, and squirrels from reaching the nests. This simple physical deterrent is a necessary measure to prevent a single nocturnal raid from decimating an entire colony.