Early birds? (8)
(Other definitions for cockcrow that I've seen before include "Dawn as signalled by male fowl" , "Dawn (literary)" , "Dawn as signalled by rooster" , "when night ends" , "early morning" .)
'early birds' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for larks that I've seen before include "Japes" , "Flyers who tweet" , "Fun and games" , "Small songbirds" , "early risers?" .)