Purple Martins have completed nesting and are now in post-breeding dispersal mode. They form large, colonial night roosts that are so large, they show up on radar in the morning when the birds disperse! All of the expanding/fading circles in the link below are dispersing martin roosts. Typical roost locations are mature woods near a water feature, usually a mid-high order river. The roost will start to form just before sunset. They can be tricky to find… but a very cool sight to see! Last year, there was a roost of about 5,000 martins that formed just south of Lost Bridge for a week or so. The largest I have ever seen was in Louisville KY, where over 30,000 Martins were roosting in the trees along the river.
7-31-16 morning radar: