their uppertail coverts and tail base have more rufous (adult female rufous can be all-green); and their chip calls are slightly lower pitched. Also see female and immature calliope hummingbird ...

tinny pit call and twitters distinct from Anna’s. Costa’s generally plainer on throat and underparts, without dusky throat spotting. See black-chinned hummingbird.

The hummingbird study that Tom Smith and Chris ... When a population of, say, lizards or birds becomes divided by geographical barriers, small changes over time will alter the genetic makeup ...