Bird — it is south of where some in flock gather (5)
I believe the answer is:
pewit
'bird' is the definition.
(pewit is a kind of bird)
'it is south of where some in flock gather' is the wordplay.
'is south of' means one lot of letters go next to another.
'where some in flock gather' becomes 'pew' (I can't justify this - if you can you should believe this answer much more).
'it' after 'pew' is 'PEWIT'.
Can you help me to learn more?
(Other definitions for pewit that I've seen before include "Lapwing" , "Bird" .)