But the forms which enter into and go out of nature are the likenesses of eternal realities modeled after their patterns in a wonderful and mysterious manner.
Identification can be a puzzle, but it's a puzzle that birders love to work on.
Actually, the concept of species is something of a puzzle in itself. Ornithologists argue at length and with surprising heat about what the word means. It's odd, because it is such a common sense, everyday notion, that everybody knows fairly well what a species is. And everybody knows that all birds belong to one species or another. It's true, sometimes the birds don't look exactly like the pictures.