Mag in part excited flier (9)
I believe the answer is:
ptarmigan
'flier' is the definition.
(ptarmigan is a kind of birdanimal)
'mag in part excited' is the wordplay.
'excited' is an anagram indicator.
'mag'+'in'+'part'='maginpart'
'maginpart' with letters rearranged gives 'PTARMIGAN'.
(Other definitions for ptarmigan that I've seen before include "Highland game bird -- giant ramp (anag)" , "Type of mountain grouse" , "Bird of the grouse family" , "Game bird living the high life" , "Grouse-like bird" .)