Dear Tweeters,
There, that got your attention!
The tiny hummingbird that visited my Skagit County feeders on the morning of the thirtieth of September came back on the evening of the first of October (yesterday, Monday). I took some better photos on Monday evening, and now I am sure that the bird was a Costa's Hummingbird. A couple of friends stopped by today (Tuesday), but did not see it. The feeders are filled and ready, so I am hoping that it comes back tomorrow.
If anyone with expertise on hummingbird ID could please look at the photos on my eBird checklists, especially the checklist of October first, it would be most appreciated if they could share their knowledge. I would love to hear any arguments as to why the bird is not a Costa's. The checklists can be found by doing a species search for "hummingbird species" in Skagit County; the location comes up as an orange pinpoint between Sedro-Woolley and Concrete.
The little hummer was dwarfed by all of the Anna's Hummingbirds that fed near it. The photos show that it has a tail that reaches to about the same length as the tip of the wings. The tail has white tips. There is absolutely no trace of tan, buff, cinnamon, or any other warm color in the plumage. The face pattern has the well-defined dark area behind the eye, with a white arc going above it and behind it. The length and shape of the bill match up with everything I have read about the bill of a Costa's Hummingbird. The rounded shape of the tail feathers and the shape of the white tips on those feathers also match up with what I have read for Costa's. 
Some of the photos show the structure of the wing quite clearly. I am guessing that there is some sort of wing formula that would help elucidate this identification, if only I could find such a thing.
Yours truly,
Gary Bletsch
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