The kind that fly, not the kind some people drive. :)
The birds that frequently visit our feeder appear to be Black-Chinned hummingbirds. One of them, a male with a black head and purplish throat, keeps watch over the feeder from a nearby juniper. If another hummingbird flies too close, or sneaks a few sips, the "sentry" dive bombs the interloper and chases it away. It's amazing to watch them as they dart and zoom across the yard. The speed of their wings (as they hover to feed) is astonishing.
This is one of the many joys we have living in our new place. I hope to nab a few photos of the tiny "jewels" in the future.