Many people wonder why so many hummingbirds can gather in certain regions and feed together on the same feeder when in other regions two birds can't get along on the same feeder. This is really dependent on the population. The less birds you have, the more one will try to dominate. When the numbers start to increase dramatically they soon realize it'll be difficult to chase away one hundred hummingbirds. They do less chasing but continue with the squeaking in squabbling. They are still angry but soon realize it's more productive to feed together than constantly chasing others.
When you first look at this image, you would think the young male on the right is overstepping his boundary with the adult male on the left. In reality the juvenile male on the right had already fought and won territory over that feeder. As the numbers started to increase in the yard with new migrant birds, the adult male on the left took it upon himself to feed from the first feeder he spotted. He arrived while the young male was feeding. The young male then pulled its bill from the feeder and was a little shocked the adult male would even dare. Needless to say, it started another battle as it typically would.
This is one reason I like to place multiple feeders around the yard. Early in the season the dominant male will try to control all feeders. It makes it more difficult if you spread the feeders apart. Later in the season it's not about breeding, but just stocking up on food for the southern journey. Early in the season one dominant male will win the rights and access to everything in the yard. You may still have other males sneak into the yard for a drink, but for the most part the dominant male will take over. When the southern migration starts, that territory shrinks dramatically. You can get countless males that share the yard, but each one will try to control its favorite feeder until they all get it sorted among themselves.
Both hummingbirds are Ruby throated, but the one on the left is an adult male, and the one on the right is a maturing juvenile male.
Northeast of Edmonton, Alberta, Canada, August 2017.