Attached is a good fact sheet from a purple martin conservation organization. The section on competition addresses your question specifically, but the whole article in very interesting. Here is a link that might be useful: Click here for Fact Sheet

Animals can be so strange....you may put all your time and effort into building just the right box, selecting a 'perfect' site, and then....nothing. Or the opposite may happen, and it will seem as if they were sitting around WAITING for you to get their new home up and going for them. I think it's different for everybody, but you will have to be PATIENT. Years ago we got a booklet from the DNR that had blueprints and general info for houses that were specific for each species. We looked it over and chose to make wood duck boxes, thinking they would have a place to nest by our pond. What we learned, in fact, was that many species simply don't care if a box is not "designed" for them...if they can get their bodies through the hole, there's nobody already at home (depending on the animal this may not matter either) and the place seems safe enough, it's a done deal. Not only will screech owls use a duck box as a day haven, they will indeed nest and rear young in them. There is a slough I frequent that has three duck boxes on it, and during one spring I discovered one particular box was home to a nest of screechies. I think the slough was dry that year, but usually this box is surrounded by about 2 1/2 feet of water...a rough first flight for any chick. I can't recall how many chicks were in that nest...I will have to try to dig out the animal album and find the photos. But they will use a duck box. When we first hung out duck boxes here at our place, I was getting frustrated waiting. It was something like three years before we finally found a nest, and then all three boxes had action!! It's worth the wait, so hang in there. But I'm still waiting for bats to use their house....I don't think they need any extra places with all the shagbark hickories. But the winner in my Crazy Nester category goes to the bluebirds at my dad's place. For the past three years, there has been a pair of bluebirds nesting in his martin house. Not a thing to be seen of any martins, but these blues are shoulder to shoulder with house sparrows and to this day I don't yet understand how they are pulling this off.

Are there any nests in the boxes? I also think they are Tree Swallows. If they are in there from last fall or summer they are probably babies that could not get out of the boxes. Tres need a ladder if you will to help them fledge from the nest. All that needs to be done is to make some deep scratches or kerfs on the inside of the box leading up to the hole to help them climb out. There is a website that will give you all the info you will ever need about Bluebirds Tree Swallows and any other cavity nesting birds. www.sialis.org We will also help any time you have questions Cathy Here is a link that might be useful: sialis.org

Put it in the most open area you have. There is a ton of information on the PMCA's website. I put up my first one this year, and I also live in MA. Be prepared to deal with House Sparrows, and Starlings (if you don't use the Starling resistant entrances) I have had nothing but House Sparrows so far. Even if you think you don't have House Sparrows, they will show up once you put up the house. I've had one pesky couple that I have had a great deal of difficulty eliminating. They are very shy since they know I'm out to get them. Nonetheless, they brought back two more with them this morning. Once they see all those entrances, they are relentless. Good luck. Here is a link that might be useful: PMCA