This hummer has been difficult to do a definite ID, even using the excellent Peterson Field Guides "Hummingbirds of North America. The unusual gorget is the problem in making an identification. The pose and lighting on this hummer does not show the usual bright to golden green on her back, but she does fit the description for a adult female Costa's, however. The following photo of the same bird shows a small patch of metallic violet-purple feathers in the lower center of the gorget, which may be present on a female Costa's.