Hope your martin houses are up. We put ours up 4 days ago and withing 30 minutes the purple martins were claiming their apartments. Only problem is that the sparrows were also. It’s a constant battle trying to keep the sparrows out. They are so aggressive. Here’s a good article on just how obstinate these little critters can be: http://purplemartin.org/forumarchives/archive/HSrevenge.htm
The Purple Martin Conservation Association is a great source of information.