On cracker, cuckoo bird (9)
I believe the answer is:
corn crake
'bird' is the definition.
(I've seen this before)
'on cracker cuckoo' is the wordplay.
'cuckoo' is an anagram indicator.
'on'+'cracker'='oncracker'
'oncracker' anagrammed gives 'CORN-CRAKE'.
(Other definitions for corn crake that I've seen before include "Grassland bird with rasping call" , "Secretive grassland bird" , "Rail nesting in hayfields" , "Elusive grassland bird" , "Secretive bird of grasslands" .)