After a recent rain, I noticed thousands of birds feeding in this field (you can only see a fraction of them in this photo). A few weeks prior, I saw thousands of bees swarming over an open field downtown ... (poor quality) video here.
I'm sure the birds were out shopping for worms the rain brought to the surface, but I have no idea why that field was swarming with bees. I don't know how well you can see the bees in that video, but they were everywhere ... and yet they never left the grassy area. It was almost as if there was an invisible barrier preventing them from flying onto the sidewalk. It was eerie!