Wild Bird Rescue has a Purple Martin house that has been very popular in years past. The trick is to allow the purple martins in while keeping house sparrows and starlings out.
Lila Arnold, one of the other rehabbers at Wild Bird Rescue, said she had been seeing house sparrows taking over some of the units, and asked if I would clean the nests out while I was here Saturday.
Sure enough, when I got here I could see three pair of martins checking out the apartments and I could also see a pair of house sparrows going in and out. I had my husband drop the house (my hands aren't strong enough to wrestle the pins--darned arthritis!) and pulled out a large house sparrow nest. I checked the other units and could see a few had the beginnings of purple martin nests.
Today I drove up to Wild Bird Rescue and there are at least 6 pairs of martins busily going in and out with nesting materials. I could also see a pair of house sparrows busily working away. At this point with the martins looking well established, I probably won't drop the house again. However, I thought about it when I saw a starling sitting on top of the house, as they can be very aggressive and have been reported to oust martins.
I think this group will be OK though. As I watched the starling, trying to decide what I should do, I noticed a couple of martins diving at him. One grabbed him and they fell to the ground, where they wrestled for a few seconds before the starling flew away, pursued by several of the martins. It appears they can take care of the starling interloper fine on their own. Bob Lindsay observed a similar mobbing on a starling last year.
I've been out since and it appears there are about 6 pair of martins and 2 pair of house sparrows in the unit. We'll see how it goes. If the house sparrows look like they are getting obnoxious, they'll have to go.