Most years the LSU AgCenter receives a few questions asking why purple martins failed to take up residence in a birdhouse provided for them.Purple martins prefer to nest around people, and we like that since they eat lots of insects. Martins are even sociable with each other – purple martin birdhouses are typically built to house a number of families.
So, what’s the problem when you put out a house and the martins decline the invitation? The following are 10 common mistakes to avoid, as compiled by ornithologist James R. Hill III of the Purple Martin Conservation Association.
1. House is too close to tall trees or in yards that are too enclosed. Air space at house height should be void of trees in at least a couple of directions for 40 to 60 feet.
2. Gardener allows other birds to claim the housing first. If the house was not used by breeding martins last year, they will be easily repelled from the entire housing complex if other birds arrive first. On the other hand, they seldom are intimidated from reoccupying the site they used the preceding year.
3. House is too far from human housing. Martins prefer to nest within 100 feet of people, where they have learned they are safer from predators (snakes, raccoons, opossums, hawks, crows, owls).
4. House is not painted white. White reflects the sun’s heat, highlights the dark entrance holes and best enhances the male’s courtship display.
5. House is opened up too early. Purple martins migrate, returning to our area by February or early March. The oldest arrive first and return to where they bred the preceding year. Last year’s fledglings show up over the following 12 to 16 weeks, beginning 4 to 5 weeks after the “scouts.”
6. Failure to open the martin housing early enough. This sounds like a “Catch 22,” considering the preceding point. At unestablished sites, the birds have to see either the open entrance holes or other martins there.
7. Allowing vines or shrubs to grow up under the house. Purple martins tend to avoid such unestablished sites because they are more accessible to predators.
8. House is not built to specifications. A compartment’s floor dimensions must measure at least 6 inches by 6 inches, and 7 inches by 12 inches is far superior. The entrance hole should be about 1 inch above the floor and be 2 inches to 2 1/4 inches in diameter.
9. House is attached to, or too close to, wires. Martins know instinctively that squirrels can gain access to the house.
10. House that cannot easily be lowered and cleaned. Gardeners need to lower the houses often to evict nest-site competitors and check on martin nestlings.