Standards for Purple Martin Housing
The novice Purple Martin enthusiast is usually unaware of what constitutes properly designed martin housing. They buy a house because it's cheap or looks good. There are a few basic design features that should be incorporated into martin housing in order to attract martins and properly manage a colony. The most important design feature is accessibility. If the housing cannot be conveniently accessed, it will usually become an expensive lawn ornament or martin slum that, ironically, ends up hurting the species it was meant to benefit by providing a breeding place for the Purple Martins' two biggest enemies - European Starlings and House Sparrows.
1. Pole Systems and Accessibility. The housing (house or gourd rack) should raise and lower vertically – in other words – without tilting over and without needing to be accessed from a ladder. These systems include rope & pulley systems, winch-cable-pulley systems, and telescoping pole systems. (For safety reasons, housing on a telescoping pole should not exceed 25 lbs. combined weight of all hardware above lower section of pole.) These systems allow the manager to safely conveniently access the housing and evict starlings and House Sparrows through trapping or nest removal. Managers who must continually climb a ladder or tilt over a heavy house to remove starling or House Sparrow nests usually give up on fighting off these two exotic species. European Starlings and House Sparrows are very abundant and aggressive. If allowed to claim Purple Martin Housing, they will develop "site tenacity" and repel investigating martins. Vertical accessibility also allow martin managers to access the martin nests without damaging the nests, eggs, or nestlings. This access makes it is possible to monitor the nests to detect problems and perform nest replacements, both of which can dramatically improve breeding success.
2. Nest Cavity Accessibility. Nesting cavities should be accessible without damaging the martin nests inside. Again, this access makes it convenient to remove European Starling and House Sparrow nests, and to access and monitor the Purple Martin nests. Access by floor removal is unacceptable because it can damage the martin nests, eggs, or nestlings. Ideally, the cavities should have access from the front or side. The door or access port should be at least 4" in diameter to allow for the insertion of the human hand.
3. Cavity Dimensions. House cavities should be at least 6" high x 6" wide x 6" deep. A depth of 10-12 inches is usually MUCH more attractive to martins and offers better protection from predators. Martins normally build their nests as far from the entrance hole as possible because they instinctively know that the nest is then more protected from predators (raccoons, hawks, and owls) that try to reach in through the entrance hole. This increased depth also helps protects the martin nests from driving rains. Gourds should be at least 8 inches in diameter, but are usually safer and more attractive to martins when they are 10-12 inches in diameter. Martin House cavities that are deeper than 6 inches are very attractive to starlings. We recommend that deep cavities be equipped with starling-proof or starling resistant entrance holes.
4. Predator Guards. Housing should be equipped with
climbing predator barriers (raccoons, snakes) and flying predator guards (owls,
accipiters) to protect nesting martins from these predators. These guards are
available commercially or can be home-made.
Courtesy of the Purple Martin Preservation Alliance