The birds!

I saw the strangest thing today as I was coming home from work. I pulled up into the road that leads to my house and there was a huge flock of birds flying in a spherical pattern above the woods at the end of the road. There was another of the same a little farther away, but not very. I ran inside to get the camera or the video camera, but when I came back out (less than 2 minutes later) they were gone! not a bird in sight! I'm not sure what kind of birds they were, but they looked like gulls. I've never seen birds fly in a sphere before. it was very odd.