This hummingbird has been visiting the feeders in my Tucson yard for at least the past three weeks. Its voice does not sound like any of the normally occurring species – being too soft for Anna's, too high and percussive for Black-chinned, and not at all like the tinkling of Costa's. I've made sonograms (using Raven Lite) of several species to compare, and I'm still puzzled (see below).
Note: you can click on any image in this blog to see a larger image.
Visually, it looks most like a long-billed Costa's, but there are features that make me think Black-chinned. It actively pumps its tail while hovering, much like Black-chinned. The answer may lie in the shape of the primaries and tail feathers, and that may require trapping the bird.
A shot that shows the primary shapes a little better.
An Anna's Hummingbird for comparison
A Costa's Hummingbird for comparison
Vocally, this bird is most reminiscent of Archilochus, especially in rhythm. I've posted a clip to the mysteries page at Xeno-Canto.
And here are sonograms that compare all the similar species.