Container a railway emptied for flier (6)
I believe the answer is:
canary
'flier' is the definition.
(canary is a kind of birdanimal)
'container a railway emptied' is the wordplay.
'container' becomes 'can' (can is a kind of container).
'emptied' means to remove the middle letters.
'railway' with its centre taken out is 'ry'.
'can'+'a'+'ry'='CANARY'
'for' acts as a link.
(Other definitions for canary that I've seen before include "Bird from an island group" , "Pet bird" , "Songbird once used to detect toxic gases in mines" , "Caged song bird" , "Bright yellow songbird" .)