Ninja sparrows

Your passage through the woods is generally attended by sufficient noise to warn birds of your coming long before you see them. They are then suspicious and ill at ease, but secrete yourself near some spot loved by birds, and it may be your privilege to learn the secrets of the forest.
Birds of Eastern North America, Frank M. Chapman, 1922

I was walking through the park yesterday in the dying afternoon light and had a freaky experience. Dark wings and bodies silently lifting off from the ground and flooding through the undergrowth like a vapor. I'd spooked scores of white-throated sparrows feeding in the dead leaves. I'd made them suspicious and ill at ease. I have to admit, they did the same to me. I'd never seen a big flock like this, and I didn't know anything like this happened in the park that I thought I knew so well. And there was something eerie about them; they looked like some kind of CGI effect, all ethereal wings and shadows. I stopped dead and did like the book says: secreted myself. The flock forgot all about me and went back to feeding. With the naked eye, I could barely even make them out. Only with the binoculars could I see that they were everywhere, all around me. The ground was alive. They were moving more stealthily than I realized sparrows ever could. Ninja sparrows, one minute they would be there right in front of me, the next they would just melt into the shrubs. Spooky. They were there again this morning when we went to check out the park. They must have decided to rest up a bit and feast before continuing south. We counted at least 50, but could hear probably 50 more, chirping 360 degrees around us.