Bend, Deschutes Co., Oregon. 28 August 2000. Photo by David Tracy.
I got these shots of a female Costa's hummingbird that visited my feeder on August 28. Sorry for the late report, but I just got my new Sibley guide and wanted to use it to check it out on some hummingbird video I had taken. I looked at a section of video taken on August 28 and realized I had reported a black-chinned that was a better match for Costa's in Sibley's new guide as well as several other references (i.e. BONA, Kaufman's Advanced Birding, various papers, online sources, etc.)
If you want any further information on the I.D., I'll copy you on my OBRC report. I also have some feedback on the bird from Nancy Newfield that I could pass along.
To my knowledge, the only other documented record of a female Costa's in Oregon was written up in American Birds (45:1153). I'm not sure if there were photographs taken of that bird. The passage from AB is quoted below:
"Costa's Hummingbird has become a scarce but annual post-breeding visitant to Oregon, but this summer a female attempted to nest. The nest with two eggs was found on the s. Oregon coast, in Harbor, Curry June 16  (Alan Barron, Colin Dillingham). Unfortunately, the next day a car antenna swiped the nest and both eggs were destroyed. The nest and destroyed egg were collected when the female was last seen on June 21 (Collected by Western Foundation of Vertebrate Zoology)."