One of the best ways to attract purple martins and enjoy these beautiful swallows in your yard is to use appropriate purple martin houses. In the eastern United States, purple martins are almost entirely dependent on artificial nesting sites, but like all birds, they can be picky about which houses they choose. The best houses will not only attract these birds, but proper construction will help keep any residents safe from poor weather and predators.
Types of Houses
There are two types of birdhouses that purple martins prefer: single structures with many compartments or individual homes arranged in a cluster. Because these are social birds, they often nest in colonies of dozens or hundreds of mated pairs. Single structure “apartment” style birdhouses feature multiple entrances leading to adjacent chambers. Tiers of compartments are popular and can provide housing for many pairs of purple martins in a small space.
Clustered arrangements of several, even dozens, of individual birdhouses can be placed together to create a compact nesting colony. The most popular style of individual birdhouses for purple martins are hollow gourds, which can be aesthetically pleasing as well as appropriately sized and spaced for the birds. Natural gourds that have been dried and treated can be used, and many manufacturers offer plastic gourd-shaped birdhouses perfect for purple martins.
Bird House Dimensions
The dimensions of a birdhouse are one of the most important factors in making it suitable for particular bird species. If the home is too small, adult birds may not be able to enter or exit, and growing nestlings could smother in inadequate space. A home that is too large gives predators easier opportunities to kill nesting birds, and larger undesirable birds may use the home to nest instead.
The best dimensions for purple martin houses are:
- Entrance hole: The diameter of the entrance hole should be between 1 3/4 and 2 1/4 inches. Entrance holes measuring 2 1/8 inches are the most popular. Crescent-shaped holes can also be effective in preventing other birds from using the houses, but purple martins have no trouble with that unusual shape.
- Entrance height: The entrance hole to the house should be 1 inch above the floor. A lower hole will not provide adequate protection from predators and weather, and young birds could more easily topple out of the opening. A higher hole will be too difficult for parent birds to enter and exit while feeding young birds.
- Interior floor area: The minimum space of the interior floor should be 6 by 6 inches, though slightly larger homes are also suitable and may be more comfortable for large broods.
- Interior height: The internal height of the house should range from 5 to 7 inches to provide enough space and ventilation for all the birds. If using gourd purple martin houses, the interior height should be 8 inches to accommodate the unusual shape and upper tapering of the house.
- Porches: Porches are not necessary on purple martin houses, but if they are used they should be 4 inches wide to allow birds to walk safely. If a railing is used as a decorative accent on the porch, it should be no higher than 5/8-inch or birds may become trapped underneath it.
Even the most well-designed birdhouse will be unsuitable for purple martins if it is not placed properly. These birds need large, open areas to feed, and any purple martin birdhouse or cluster of houses should be placed in the center of an open area at least 30 feet away from any other trees or structures. At the same time, purple martins are accustomed to living near humans, and the most frequently occupied houses will be within 120 feet of human habitation. Placing the house near a permanent water source such as a pond, lake, or stream is also effective in encouraging purple martins to take up residence.
The height of an installed purple martin house should be between 12–20 feet. The home should be placed at the upper end of that range if there are trees or bushes nearby, but if the area is very open then shorter homes will be just as suitable.
Managing Nesting Colonies
Purple martins have become accustomed to and dependent on artificial nesting sites over centuries of association with humans. Because of this, anyone putting up purple martin houses must be prepared to monitor those houses to keep them suitable. Both European starlings and house sparrows can aggressively compete with purple martins for nesting sites, and constant checking of available houses is necessary to remove unwanted nests and give the martins better opportunities to thrive. Purple martins will not abandon nests that are regularly checked, though care should be taken to avoid undue stress on incubating birds or young hatchlings.
Tips for Houses
To choose the best birdhouses for purple martins and ensure they can use the structures safely:
- Paint homes white for the best heat reflection and to attract purple martins more easily.
- Ensure wooden homes have walls at least 3/4-inch thick for adequate insulation.
- Add a layer of insulation to the roof of plastic or metal homes to help regulate internal temperatures.
- Check that all compartments have adequate ventilation and drainage holes.
- Avoid designs that include entrance perches, as these will only give predators easy access.
- Use pole baffles to deter predators such as snakes, raccoons, and cats.
- Choose telescoping poles that can be raised and lowered easily for regular house checks.
- Add door plugs to each compartment to prevent winter roosting and early nesting of starlings and sparrows.
- Consider a locking mechanism on the pole if necessary to keep it from twisting in the wind.
Adding purple martin houses to the right backyard habitat is a sure way to attract these beautiful swallows to your neighborhood. By choosing safe, effective houses, you can encourage purple martin colonies and minimize trouble from unwanted tenants.