Enter the duck in the list as “farmyard bird” (7)
I believe the answer is:
rooster
'farmyard bird' is the definition.
(I've seen this before)
'enter the duck in the list' is the wordplay.
'enter the duck' becomes 'o' (I can't justify this - if you can you should give a lot more credence to this answer).
'in the' is an insertion indicator.
'list' becomes 'roster' (roster is a kind of list).
'o' put within 'roster' is 'ROOSTER'.
'as' is the link.
Can you help me to learn more?
(Other definitions for rooster that I've seen before include "Early-morning caller" , "Morning caller" , "Male domestic fowl (US)" , "Toreros (anag.)" , "Cockerel (mainly US)" .)