Purple martins in Texas, USA

This video is called Purple Martins at Highland Mall, Austin, Texas 2012.

From Associated Press:

Thousands of birds nest near abandoned Austin mall

Published: July 25, 2014 10:12 AM

AUSTIN, Texas – — Outside an abandoned Austin shopping mall is a little-known visual phenomenon to rival the bat flights from the downtown Congress Avenue bridge.

Six oak trees stand in a bank parking lot on the north side of Highland Mall. For decades, every July, birds called purple martins have flocked to the trees by the thousands to roost for the night. And the spectacle draws dozens of bird-watchers each night.

The birds, which are the largest North American swallow breed, migrate to the spot in July and August as they head north from Brazil to breed. The Purple Martin Conservation Association says flocks have shown up on National Weather Service radar.

The Travis Audubon Society holds watching parties from 8 p.m. to 9 p.m. each Friday and Saturday evening in July.