In a good year a bird is a bird (9)
I believe the answer is:
gyrfalcon
'bird' is the definition.
(gyrfalcon is a kind of bird)
'in a good year a bird' is the wordplay.
I cannot really see how this works, but
'a' is within the answer.
'good' could be 'g' (abbreviation) and 'g' is present in the answer.
'year' could be 'yr' (abbreviation) and 'yr' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'is a' acts as a link.
Can you help me to learn more?
(Other definitions for gyrfalcon that I've seen before include "Fly, garcon (anag)" , "See rare bird" , "Large bird" , "Making this bird" , "Arctic bird of prey" .)