I have my ugly old hummingbird feeder out, and it has attracted a variety of species, Calliope, Rufous, and Ruby-throated. According to my Sibley bird book, this part of Montana is out of range for the Ruby-throated, but the only other possibility is the extremely similar Black-chinned, and we also are out of range for that. Obviously the bird in the image does not have a red throat, but the bird book does show this as a variation. And based on some out-of-focus images of a different bird that show a bright red throat, I'm going with Ruby-throated.

Calliope

Rufous

Ruby-throated (maybe)