I think you should try sierra's suggestion first and if you can't make it B&W enough try this:
I duplicated the layer twice,
did poster edges on one as sierra suggests. On the posterize layer, since I made different edge thickness and intensities, I had more grey. I used color range and masked that out.
then added a threshold layer such as you did, and changed the blend mode to divide. On the threshold layer, I did the select>color range for the white (should have done black)
On the third layer I made a drastic levels adjustment to bring the wings up as dark as possible.
I then did filter>poster edges with edge thickness and intensity at half and posterization at full.
I did color range and selected for black and masked the selection.
Finally, I masked out everything on that level except the wings.
Then I made a png and did color range one more time for the white. I put a color layer below so you can see. There is some white residual. If that's a concern, you can be more thorough with the color range selection. I had fuzziness set kind of low and I didn't just select black that second layer (which I did on the 3rd). You'll probably have to go in by hand and erase or mask some things anyway. The poster edges filter finds edges where you probably don't want them so just go ahead and delete or mask those.
Here's a simple channels solution (I've used it) to the "get the white out" from this kind of image -- once you get it to lines that is:
http://krysjez.wordpress.com/2009/02/22/extract-lineart-in-8-simple-steps/
Anywho, that's how I would do this. It isn't that much different from sierra's, just has the color and white taken out. Guess it depends on what you're looking to use it for. :mrgreen: