Spectacular! I just looked up the difference between Tree Swallows and Purple Martins. For years I have been calling the Tree Swallows Martins. They don't seem to mind because at least two nests of them are raised here every year. Can you tell us more about your rack, how it operates, and if the houses are painted gourds or terracotta, etc. If raising the rack doesn't need too much muscle, I think I could maintain one of these colonies. Would this work on a flagpole already installed? We are on a hill above marshes on the Willapa river, and enjoy watching the birds as they perform "skeeter patrol". We have not seen nearly as many of the birds this year. I hope it's because there has been less rain this summer, and not because of some campaign to spray spartina.