Bird sound from hen dropping large eggs (6)
I believe the answer is:
cuckoo
'bird' is the definition.
(cuckoo is a kind of bird)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for cuckoo that I've seen before include "that can emerge at hourly intervals" , "It takes over other birds' nests" , "Hourly you might hear this" , "fool" , "Slightly crazy -- bird" .)