Mystery hummingbird

Hummingird in iochroma
Hummingird in iochroma.

The iochroma is flowering, and that means the hummingbirds are back. I like to photograph them, in part because this particular iochroma is right outside my study window, and it makes a nice diversion from my literary work, and also because it’s challenging to freeze the speedy little hummers in photos.

But what kind of hummingbird is this? I’m not the bird identifier that Charles Hood and Jonathan Franzen (my companions on a Catamaran catamaran a while back) are. I get frustrated because bird books tend to feature adult males. I suspect this one might be immature, or maybe even a female. In any case, try as I might, I cannot find a reference to California hummingbird that has a yellow patch on its head.

Any birders out there?