Preserve a track for singer in cage? (6)
I believe the answer is:
canary
'singer in cage?' is the definition.
(caged bird)
'preserve a track' is the wordplay.
'preserve' becomes 'can' (canning is a kind of preserving).
'track' becomes 'RY' (abbreviation for railway).
'can'+'a'+'ry'='CANARY'
'for' acts as a link.
(Other definitions for canary that I've seen before include "Songbird once used to detect toxic gases in mines" , "A yellow singing cage-bird" , "Bird from an island group" , "grass" , "Caged song bird" .)