Here’s a small flock of waterfowl, same day, same location. I shot this with the intent to compare, they’re the only birds I saw that morning. These are much larger than those drones.
Yes it looked like a close flock of birds but the guy is a drone flyer and said he did hear the faint sound of drones each time those groups flew over his head. And they did seem to be flying too fast for birds. A drone flyer should be able to...