We had these birds at my house in Southern California where I grew up. They are very aggressive to other hummingbirds. It's actually fun to watch, they'll do this aerial joust sort of thing where they each rise up vertically to 50 or more feet and then dive down in a J shape and go right at each other. I've never seen them colide so I assume they're just trying to peck each other in passing, but they go FAST! Very flashy and a bit mean to one another.
(Hi, I'm a long time reader here, just never posted. Suggested a few images before though.
)