At the end of the nesting season Purple Martins leave their apartment houses and gourds and form large flocks. The flocks may number in the hundreds of thousands of birds. They return to a communal roost at night and fan out during the day to feed.
There is a large roosting location near Denton, in North Texas.
The Purple Martin Conservation Association maintains a list of roost sites.
It is a spectacular view when the martins return each evening. Take the family if you have the opportunity to visit a roost site.