Bird, some scoter, naturally (4)
I believe the answer is:
tern
'bird' is the definition.
(tern is a kind of bird)
'some scoter naturally' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'TERN' can be found hidden inside 'scoter naturally'.
(Other definitions for tern that I've seen before include "Seagull" , "Long-winged aquatic bird" , "Gull-like seabird" , "Small seabird with forked tail" , "Small gull with forked tail" .)