The adult male Lucifer Hummingbird is similar in plumage to the adult male Costa's, but is easily separated in the narrow zone of overlap between the two species by its strongly decurved bill and forked tail. The female Lucifer is strongly buffy below and has a decurved bill and forked tail. The female Costa's is similar to the female and immature Anna's, but typically is smaller, with a cleaner throat and whiter underparts. Archilochus hummingbird females are also similar but tend to have streaked throats. Female Costa's are separable also by subtleties of tail pattern and call notes.