Shot mating pair -- missing one grouse (9)
I believe the answer is:
ptarmigan
'grouse' is the definition.
(ptarmigan is a kind of grouse)
'shot mating pair missing one' is the wordplay.
'shot' is an anagram indicator.
'missing' suggests deleting specific letters.
'one' becomes 'i' (Roman numeral).
'mating'+'pair'='matingpair'
'matingpair' with 'i' taken away is 'matngpair'.
'matngpair' anagrammed gives 'PTARMIGAN'.
(Other definitions for ptarmigan that I've seen before include "Type of mountain grouse" , "Grouse-like bird" , "Northern game bird - map rating (anag)" , "Arctic grouse" , "Bird of the grouse family" .)