Socialist survey on a bird (7)
I believe the answer is:
redpoll
'a bird' is the definition.
(redpoll is a kind of bird)
'socialist survey on' is the wordplay.
'socialist' becomes 'red' (socialism is often associated with the colour red).
'survey' becomes 'poll' (polling is a kind of surveying).
'on' means one lot of letters go next to another.
'red'+'poll'='REDPOLL'
(Other definitions for redpoll that I've seen before include "Bird" , "cow" , "finch" , "Flyer" .)