My Dad tried to have a purple martin community for years, when I was growing up. He did get them one year, but they never returned. I have read that having purple martin homes is like having a garden. To successfully keep a purple martin community you actually have to help them along. They will just up and leave, for example, if their nests get too wet. Or the nests get bugs or wasps in them. I do know you were right to put the jumpers back, so that wasn't the problem. I don't know how long they stay in a season though.