Costa's Hummingbird (female)

That is what I was leaning towards - thanks much, Liam! And thanks to Jemma for your input too!

Tail is too short and consequently the primary projection too long for Anna's. That, along with the extensive supercilium and curved bill make this a Costa's, I do believe.

I think the breast and supercilium look far too white and clean to be an Anna's - we have lots of juvenile Anna's around, and this hummingbird looks quite different.

looks like a young Anna's Hummingbird.