Ogre beginning to eat diver (5)
I believe the answer is:
grebe
'diver' is the definition.
(diving bird)
'ogre beginning to eat' is the wordplay.
'to eat' says the answer is hidden in the clue (I've seen 'eaten' mean this).
'GREBE' is hidden within 'ogre beginning'.
(Other definitions for grebe that I've seen before include "I'll dive in" , "Diving bird which may be crested" , "Swimmer" , "Small bird that builds floating nests" , "Diving water bird" .)