Warbler's eaten such nuts (9)
I believe the answer is:
chanteuse
'warbler's' is the definition.
Both the definition and answer are singular nouns.
Perhaps you can see an association between them that I can't see?
'eaten such nuts' is the wordplay.
'nuts' indicates an anagram (nuts can mean crazy).
'eaten'+'such'='eatensuch'
'eatensuch' anagrammed gives 'CHANTEUSE'.
Can you help me to learn more?
(Other definitions for chanteuse that I've seen before include "Female cabaret singer" , "Tunes ache for this French woman singer" , "Female popular singer" , "She sings popular songs" , "A French female nightclub singer" .)