Dark hen's dicky bird (8)
I believe the answer is:
redshank
'bird' is the definition.
(redshank is a kind of bird)
'dark hen's dicky' is the wordplay.
'dicky' is an anagram indicator (dicky can mean ill or non-functioning).
'dark'+'hens'='darkhens'
'darkhens' with letters rearranged gives 'REDSHANK'.
(Other definitions for redshank that I've seen before include "Leggy bird" , "22 [FT SETTER]" , "Wader" , "Wading bird" , "Highlander" .)