Diving bird’s culpability, eating most of fruit (9)
I believe the answer is:
guillemot
'diving bird's' is the definition.
(type of diving bird)
'culpability eating most of fruit' is the wordplay.
'culpability' becomes 'guilt' (someone culpable for something is guilty of it).
'eating' indicates putting letters inside.
'most of' means to remove the last letter.
'fruit' becomes 'lemon' (lemon is a kind of fruit).
'lemon' with its final letter taken off is 'lemo'.
'guilt' enclosing 'lemo' is 'GUILLEMOT'.
(Other definitions for guillemot that I've seen before include "Diving bird" , "Fisher" , "Diver" , "cliff-ledge nester" , "An auk" .)