Today, outside a train station, I threw a piece of cookie on the ground. Immediately, a flock of pigeons descended on it.
Among the several dozen grey and white pigeons was one brown pigeon. After a few seconds of participating in the melee, the brown pigeon emerged, sans cookie piece, and flew to the top of a traffic light. A few minutes later, the rest of the birds flew to the other side of the street. The brown pigeon didn't join them while I was out there. It remained perched on the traffic light.
Maybe the brown pigeon is routinely bullied by the other pigeons. Maybe it's just smarter than they are and didn't want to crawl over and under them for cookie crumbs. Maybe there were other birds that removed themselves from the ruckus before it ended, and I didn't notice them because they looked like the rest of the flock.