Mischievous activities for early risers (5)
I believe the answer is:
larks
'risers' is the definition.
(I know this)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for larks that I've seen before include "Small songbirds" , "Fun and games" , "Frolics" , "Early birds" , "High jinks" .)