This immature ruby throated humming bird has the feathers of another hummer stuck to the tip of its beak! They are very, very aggressive to each other and fight in the air and at the feeders at our home here in Southeastern Missouri all the time. Their feathers actually look quite ragged at this time of the year because of all the strikes they have sustained from other hummers. It is a wonder that they even get a good feeding at the sugar water feeders because they are constantly buzzing each other as they attempt to feed.
The focal length that I use when shooting the hummers in flight is so small, around 3 inches circumference, that the second bird you see here is only about two inches out of the focal area.
Nikon D40X with Nikkor 300mm VR lens on manual focus