I have at least four hummingbirds visiting the feeder. I've seen two males visiting and feeding at the same time but the two females I saw at the same time were battling. Maybe I have more visiting but they're so quick it's hard to tell any differences.
I've had some questions on how I took these photos so I'll share that info. I use my Canon 100-400mm IS zoom lens. With the multiplyer factor of my 40D, the lens zoomed all the way is the equivalent of 640mm. I also have my 550 EX flash on the camera. The first photo of the female in flight I had the camera set at the normal synch speed of 1/200th of a second, that's why the wings were blurry. The flash was set at -1 2/3 stops underexposure so the flash light wouldn't overpower the natural light. There was no flash used on the male sitting at the feeder. On today's photo I had the flash set on the high speed synch mode so I was able to set the shutter speed at a lot faster 1/1000th of a second, which helped freeze the wings a little more. The pic is a tad over exposed but it was my first attempt at high speed so I'll be out there practicing more as the summer progresses.
I have the feeder set on my deck rail which is about 30" high, I'm standing about ten feet away with the camera looking down. The soft green background is my out of focus lawn, I shoot wide open at f5.6 so that helps with keeping the background soft.