Bird gone, so sow gets upset (4,5)
I believe the answer is:
snow goose
'bird' is the definition.
(snow goose is a kind of bird)
'gone so sow gets upset' is the wordplay.
'gets upset' indicates anagramming the letters (I've seen 'getting upset' mean this).
'gone'+'so'+'sow'='gonesosow'
'gonesosow' anagrammed gives 'SNOW-GOOSE'.
(Other definitions for snow goose that I've seen before include "Gregarious Arctic bird" , "birdie" , "Arctic denizen" .)