Bird in difficulty (4)
I believe the answer is:
knot
This clue is a double definition.
'bird' is the first definition.
(knot is a kind of bird)
'difficulty' is the second definition.
(I've seen this before)
'in' acts as a link.
(Other definitions for knot that I've seen before include "Tie (or what is put in one?)" , "that's sometimes in wood" , "Bird; hard part in wood" , "Rope fastening" , "Hard round cross-grained piece in wood" .)