I had hummers nesting in a lilac bush once. One of my cats was queen of the neighbourhood and only bowed to one particularly large Tom, but the hummers didn't put up with her. I witnessed one fight that was amazing. The two hummers were flying in figure eights, alternating smacking the cat in the back of the head on each, or at least every second, pass. It got to the point where she was lying on, nay, hugging the ground and wailing. I had to break it up. She left the hummers alone after that.