A bit of fun for an early riser (4)
I believe the answer is:
lark
I believe this is a double definition.
'a bit of fun' is the first definition.
(I've seen this before)
'an early riser' is the second definition.
(I've seen this before)
'for' acts as a link.
(Other definitions for lark that I've seen before include "Early riser" , "Bird; frolic" , "jolly occasion" , "Jape; bird" , "in-flight performer" .)