Willing sort of bird (4)
I believe the answer is:
game
I believe this clue is a double definition.
'willing' is the first definition.
(game can mean willing to do something)
'sort of bird' is the second definition.
(Other definitions for game that I've seen before include "Hunted wild animals" , "Competitive activity with rules" , "What might get hung" , "See 8" , "Willing; recreation" .)