Part of great skua's diet? (4)
I believe the answer is:
eats
'diet?' is the definition.
(eats can mean food)
'part of great skua's' is the wordplay.
'part of' says the answer is hidden in the clue.
'EATS' is hidden within 'great skuas'.
(Other definitions for eats that I've seen before include "Ingests" , "Takes nourishment" , "Sate (anag.)" , "Tuck" , "Is not any faster" .)