My parents put up a hummingbird feeder on their land in New Mexico, and it soon became the site of intense hummingbird battles for food among the three local hummingbirds. So they put up two more hummingbird feeders, and the hummingbirds would rotate all day long, fighting over the first feeder, then the second, and then the third. Hummingbirds are insanely aggressive, so much so that the Aztecs believed a warrior who fought fiercely and died in battle would meet his reward in reincarnation as a hummingbird.
This video has some audio with people talking, but I put the audio on mute. I highly recommend emulating this decision. The decision rewarded me immediately with silent, gorgeous, slow-motion footage, but rewarded me even more generously later on in the video, when the scientists start shooting lasers at the hummingbirds for no discernible reason. (You think I'm kidding, but I'm not.)
Of course the reason would have been discernible if I had listened to the person explaining it, which is why I recommend putting the audio on mute. Since I didn't know the reason, I got to make one up. Some things are just too interesting to bother with the real explanation. My conclusion is that these scientists are training the hummingbirds to take on Al Qaeda, and/or armies of giant robots.