Thanks! I'm glad you noticed it. I specifically set out with these poses in mind, and literally the first lines I put down on the page in the initial sketch were the curves of their spines and their relative positions - very little changed about the basic composition from there on out.
Look closely at the hind leg on her left side. That's actually the wing and shes leaning on her right. (Hard to explain mirroring...) So yeah. Her other wing is there but her hind right leg is underneath her. And yes I'm speaking of Derpy.
The wing is the shape behind her right shoulder. I know, it looks a little like her lower hind leg because you can only see it edge-on at this angle, and her leg is meant to be hidden under her body. I should have made it slimmer to make it more obvious what the shape was.
Fair comment. The shape is ambiguous and I can see how it's easy to interpret it as a leg, even though I intended it to be the wing (and even thought "I should make that bit clearer" while I was working on it, then forgot all about it). I may go back and fix it up a little. Thanks for your critique though - that's how one improves, after all.