Video shows the unnerving scene at a shopping center in Burleson, a suburb of Fort Worth, on January 24.
Tracy Miller was in the parking lot during the swarm.
"The grackles had taken over this parking lot for several days prior to me shooting the video. It was truly terrifying with them swarming like flies. They were everywhere: rooftops, cars, on the ground, in the trees. The sky was abuzz with them all, and they were so loud!" Miller told Storyful.
The Houston Audubon website says great-tailed grackles "tend to congregate in large flocks and prefer shopping centers and fast-food store parking lots where there's trash for food and trees or light posts for perching."