Nuts for a bird (6)
I believe the answer is:
cuckoo
This clue is a double definition.
'nuts' is the first definition.
(I've seen this before)
'bird' is the second definition.
(I know that cuckoo is a type of bird)
'for a' acts as a link.
(Other definitions for cuckoo that I've seen before include "Mad - layer of eggs in another bird's nest" , "Hourly you might hear this" , "Bird which lays eggs in others' nests" , "It takes over other birds' nests" , "Bird with distinctive cry" .)