Martins have strong site fidelity. Once they nest at a place they will stay there as long as they can. As long as predators don't run them off, or trees don't grow to close, they will stay. The more the merrier for them.
If it is allowed I will post a link to the forum that shows photos of his set up. You have to keep in mind that each of those alluminum gourd rack and pole combos cost a little of $400.00 each. The gourds range from $12-$15 each.
If you can keep the sparrows, starlings, and other predators away. Your colony will continue to grow as long as you add housing.
http://www.purplemartin.org/forum/viewt ... highlight=

