One bird eaten by another one (5)
I believe the answer is:
heron
'one bird' is the definition.
(heron is a kind of bird)
'eaten by another one' is the wordplay.
'eaten by' says the answer is hidden in the clue.
'HERON' is hidden within 'another one'.
(Other definitions for heron that I've seen before include "Tall wading bird" , "Bird of the Rhone, strangely" , "Long-legged long-necked wading bird" , "Wading bird with long neck and legs" , "Graceful grey bird with long neck" .)