Frederick,
I own a period mirror simlar to the one illustrated. The majority of the phoenix and all of the branch are carved from the board that is used to make the crest. The head and neck wood is glued on and stands proud of the surface of the crest.
If I can help with more information, please let me know.
While I have seen numerous reproductions of this style of mirror made in curly maple, I have only seen a few, small, "country" examples made in the period. I believe that this was probably due to the fact that the vast majority of mirrors, including those with American labels, were imported from Europe. PSP