Reminds me of the swifts at Chapman school in Portland. It's fun to see.
We have a big flock of swifts that swirl around the tall brick chimney that stands high above the elementary school behind my house. It is pretty spectacular to see them, at dusk, swarming around, waiting their turn to get into the chimney.
Livin's mostly wasting time, and I waste my share of mine
I am a breathing time machine
You should be able to find large flock of European Starlings across all of the lower 48 (they're introduced). I see the largest flocks in winter near agricultural fields. The flocking behavior seems most pronounced in the very late afternoon as the birds head back to their roost.