I'm fairly certain we have a pair of hummingbirds nesting/living in one of the trees in front of our house. For several weeks, I've been hearing a high pitched chip chip sound, but thought it was bushtits or sparrows and didn't pay much attention to it. Today, I confirmed that it's hummingbirds. Several crows were having a huge fight a little while ago. They came flying by and nearly crashed into my office window. One of them landed in the tree on the west side of our driveway. I immediately started hearing the chip chip sound again so I peeked out. The tiny little hummingbirds were going at the crow and trying to drive it away! They were zooming all around and dive bombing the crow. It's amazing how aggressive small birds can get when defending their territory. I'll go outside later and see if I can find any signs of a nest.