I thought it was a flock of birds, but it disappeared and then reappeared

It looked like maybe 100 white birds flying together but not in a formation. Just in a blob that changed shapes. I first noticed it as white/gray Birds. Then it disappeared. Maybe 1 minute later it reappeared in the same location (Except I was closer because I was going 60mph). I was able to get a short 30 second video the 2nd time I saw it. It kept changing shape and didn't not look like normal bird flock behavior. This was at the beginning of a runway for the military base in the middle of the day, sunny weather. The white of the "birds" seemed reflective with a dark gray contrast.