A bird with extended wings is not natural (7)
I believe the answer is:
stilted
'not natural' is the definition.
(I've seen this in another clue)
'a bird with extended wings' is the wordplay.
'a bird' becomes 'stilt' (stilt is a kind of bird).
'with extended wings' becomes 'ed' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'stilt'+'ed'='STILTED'
'is' is the link.
(Other definitions for stilted that I've seen before include "Awkward" , "Artificially formal or contrived" , "Unnatural sounding and overformal" , "Stiff and unnatural" , "Stiff, self-conscious" .)