The old adage says that patience is a virtue, but this must be amplified exponentially when applied to the prospect of attracting purple martins in hopes of beginning a new colony. Many good people with the best intentions have spent a lot of money on purple martin birdhouses, and invested even more in time and sweat to erect them, only to give up and abandon the birdhouses after one or two fruitless seasons. The fact is that purchasing and placing a purple martin birdhouse is just the tip of the iceberg. In my very humble opinion, if that were all it took, it would not be a very engaging hobby. There is much more to it, and for many people, purple martin landlording becomes much more than a hobby, often growing into a passionate and rewarding endeavor.
Having put in the effort to place a high-quality purple martin birdhouse in a favorable location, the neophyte landlord then needs to protect the property from nuisance birds. The two most common examples are starlings and house sparrows. These birds are not native to North America, so the law does not protect them. Using starling-resistant entry holes will largely mitigate the problem posed by starlings nesting in purple martin birdhouses, though they may still harass the martins.
Unfortunately, any entrance that will allow purple martins will also allow sparrows. Many very successful purple martin landlords trap and shoot sparrows. Over time, the sparrow menace will diminish to a very low level. Other landlords, who are unwilling or unable to kill the sparrows, will trap them, but then they will just clip the wings and release them. By many accounts, this does reduce the sparrow problem, but not as effectively, as it does not guarantee a reduction in local house sparrow population. However, it is possible that clipping the tail as well as the wings will make house sparrows less attractive, and therefore less successful, as mates for other sparrows.
The worst thing a purple martin landlord can do about starlings and sparrows is nothing. Anyone who puts up a purple martin birdhouse and responds to these pests with inaction is quite possibly, even likely, doing more harm than good for the martins.
Thus far, there is a good purple martin birdhouse in a good location. A caring, vigilant landlord is performing nest checks at least twice weekly to ensure there are no unwanted "visitors". There have been martin sightings in the area - maybe even active colonies nearby. Yet, the entire season passes without a single pair of martins nesting in the nice, new birdhouse. What is the missing ingredient? Once again, it is patience. With luck, some young purple martins will see the birdhouse when they are flocking together before their long fall migration to South America. Possibly, they will remember it when they are looking for a nesting site next season.
Most successful purple martin landlords had very humble beginnings. Waiting at least two or three seasons just to get the first pair or two of nesting martins is the norm. After those first couple of pairs adopt the purple martin birdhouse, it is a little bit easier to keep them. Purple martins will often return to nest in the same martin house they used the last year. Of course, a responsible purple martin landlord must keep the birdhouse clean and in good repair, all the while continuing to keep pests and predators away.
As a helpful mnemonic device, I have developed the five "P's" that form the basis for attracting and maintaining a successful purple martin colony:
1) Placement of the birdhouse. It should be from 30 to 120 feet away from human housing, and at least 40 feet away from any tree that stands taller than the fully elevated purple martin house.
2) Protection from pests and predators. Use starling-resistant entry holes, and get rid of house sparrows, one way or the other.
3) Patience.
4) Patience.
5) Patience.