wert and wast are archaic forms of "be." Wert is second-person singular past, and wast is first and third-person singular past. So you're correct, the modern-day version of the Shelley line would be "Bird you never were," or, to put it another way "you were never a bird."

Shelley doesn't mean that the bird literally isn't a bird; he's calling it (metaphorically) a spirit in the poem and saying that it's not a bird to emphasize his point. You can find a longer analysis of "To a skylark" at wikipedia, although I can't vouch for its accuracy. http://en.wikipedia.org/wiki/To_a_Skylark

Oh, sorry for writing that so ... excessively simplified, gail. :)

I like jawing about a language that is not related to software or programming, so I wast happy to find a kindred spirit - perhaps Shelley meant "wert" in the subjunctive; making the phrase poetically ambiguous..Apparently one could and did say also, "Thou wast."

I think that birds have been used by most of the major poets metaphorically (Frost's OVENBIRD), G M Hopkins (THE WINDHOVER), Hardy, Yeats, and of course, Aristophanes.

and Keats, too. He's one of my favorites.

dont forget Poe.

How could I forget Poe ?I wast being sloppy. Nevermore!

Wendell Barry writes a lot of bird poems too. And in French, Prevert has a few that are nice.