Pale-faced, like a bird (5)
I believe the answer is:
ashen
'pale-faced' is the definition.
(I've seen this before)
'like a bird' is the wordplay.
'like' becomes 'as'.
'a bird' becomes 'hen' (hen is a kind of bird).
'as'+'hen'='ASHEN'
(Other definitions for ashen that I've seen before include "Deathly pale" , "pasty" , "Looking pale from illness" , "lacking in colour" , "Grey-faced" .)