Thousands Of Swarming Birds – Is This Normal?

So I know birds flock together to go south and things like that, but this was just ridiculous. I heard this chirping sound and looked out the window to find thousands upon thousands of little black birds swarming through my backyard. I grabbed my camera and took some footage. At one point there were so many of them that they nearly blacked out the sky. Is this normal? I don’t know much about birds but you don’t see this too often. It looked like a scene out of Alfred Hitchcock’s “The Birds.” Here’s the video.