The bird file, you'll find "Duck" in (7)
I believe the answer is:
rooster
'the bird' is the definition.
(rooster is a kind of bird)
'file you'll find duck in' is the wordplay.
I cannot quite understand how this works, but
'duck' could be 'o' (resembles zero - 'duck' in cricket) and 'o' is found in the answer.
The remaining letters 'roster' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for rooster that I've seen before include "American cock" , "American cockerel" , "So retro (anag.)" , "Male domestic fowl in USA" , "Male hen" .)