Hummingbird sighting

I heard the hum first, and I was sure I knew that hum, but oddly, it was coming from the treetops. I stopped and stared up at the Manitoba maples behind the garage, and sure enough, among the topmost branches, a hummingbird was darting and hovering, and occasionally perching. I'm not sure I've ever seen one perch. After a moment it came down almost straight at me, fast, with wingbeats slow enough to look like a rapid flutter instead of a blur, and no hum. Then it veered off and hovered and perched, hovered and perched its way through the chokecherry bush-tree. At one point I had quite a clear view, and I noticed creamy-white corners on its tail. Checking the bird book, I decided it must be a female, and in this area, almost certainly a ruby-throated. The last I saw of her, she was heading west through the tops of the next row of Manitoba maples. I wonder what she was getting up there. Sap from the aphid damage?