Martin Housing System Selection Criteria
Before purchasing or constructing a Purple Martin House or starting a system, please consider the following criteria.
- Vertical Accessibility
- Height and Pole Installation
- Compartment size
- Compartment accessibility
- Entrance holes
- Material suitability
- Use of predator guards
- Other recommendations
Martin housing should raise and lower vertically on a telescoping pole, lanyard, or winch system. Housing will need to be lowered—sometimes on a daily basis—to remove House Sparrow and European Starling nests. Regular monitoring of active martin nests is essential; landlords who do not monitor their colony will not know if they are losing martins to snakes, owls, hawks, parasite infestation, weather, etc. Early detection allows landlords to fix problems before they affect the entire martin colony.
Height and Pole Installation
The recommended pole height is 12′-20’. The higher the housing is placed, the more susceptible it is to wind damage. Usually, a height of 13′ is the average most landlords use to prevent the pole from being damaged by the wind. Poles should be set in concrete, with 18”-25” below ground and the concrete base wide enough to prevent it from shifting in the ground. Many manufacturers offer mounting sockets or stakes so that landlords can relocate or remove their poles to a new location.
The minimum size for compartments is 6” x 6”, but research has shown that larger compartments (measuring 7” x 12” from front to back) offer greater protection from predators and the elements, and will keep nestlings more comfortable. Gourds should be no less than 8” in diameter, with gourds in the 10-12” range being ideal. Adult martins are 8” long, so compartments must be large enough to accommodate 4-6 nearly grown nestlings and both parents. Houses with smaller rooms can be remodeled to offer larger, two-room suites.
Access to individual compartments during the nesting season is essential, allowing for monitoring, trapping and/or removal of House Sparrow and starling nests or other predators. Access doors can be added to natural gourds as well if they do not come with them.
Traditional round entrance holes are generally 2-1/8” in diameter, but a range between 1-3/4” and 2-1/4” is acceptable. Round entrances should be placed 1” to 1-1/2” above the floor or porch. The crescent, starling-resistant hole (1-3/16” tall x 2-3/4” to 3” wide) should be placed so the bottom of the entrance is flush with the compartment floor, or not more than 1/4” below it. When using gourds, a porch is not really necessary but when using a starling-resistant entrance, you may wish to offer a porch. There are other entrances as well that offer similar protection so do some research before installing them.
Aluminum, thick plastic, wood, and natural gourds are all suitable materials for martin housing, provided that the exterior of the house is white in color. White reflects heat, keeping housing cooler in hot temperatures. Wooden housing should be made from untreated material only. Wood 3/4” thick will provide better insulation against heat and cold. Cedar, cypress, or redwood works well. Plastic houses and gourds should be of thick (preferably UV-resistant) material, and should not allow light to filter through the walls. Transparency creates a “greenhouse effect”; the heat can be deadly for nestlings. A layer of insulation in the attic of plastic or metal housing will protect martins during periods of extreme temperatures.
Use of Predator Guards
Predator guards should be installed on all active housing. Any type or size of pole, wood or metal, is easily climbed by snakes, raccoons, and squirrels. Pole guards are commercially available, but landlords can also make their own. The top of the pole guard should be at least 4’ above ground; if it’s lower, large raccoons and snakes may bypass the guard. Aerial predators like hawks, owls, and crows commonly raid martin housing. Conventional 6” x 6” compartments do not offer much protection from these predators, who can reach nestlings in shallow rooms. Larger compartments will allow martins to build their nests further from the entrance, and out of a predator’s reach. All housing—even housing with deep compartments— should be equipped with an external owl guard. If commercial guards are not available, landlords can fasten hardware cloth (2” x 4” mesh) to the outside of the house or gourd rack, creating a protective cage that can be removed for nest checks.
Newer and better martin housing continues to evolve to improve the purple martin housing situation. Depending on your geographic location, it is always prudent to check your area to see what is working best for the local martins. What may appear the best in one geographic area is not always suitable for yours. Purple martins in the northern areas require housing with top insulating qualities so aluminum or plastic housing may not be suitable unless it is retrofitted. All of the above recommendations may be further fine-tuned due to geographic location. Just because a housing system is expensive should not be the only criteria for housing system determination. Nor should the cheapest be chosen as you will have to upgrade or change your housing sooner or later. WORST yet is cheap housing that will not stand up to poor weather conditions or predation.
Purple Martin housing, equipment and accessories are readily available online as well as through local retailers. The Housing recommended by the PMCA and Nature Canada is an excellent way to start your colony in Ontario. The OPMA has had excellent success with this setup style. A large Purple Martin site at Holiday Beach, Ontario and Colchester Harbor, Ontario were started with a similar setup. Other OPMA members have had great success with this.