The ultimately early bird? (3)
I believe the answer is:
egg
'early bird?' is the definition.
(I've seen this in another clue)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for egg that I've seen before include "Reproductive cell" , "Reproductive part" , "Hen fruit" , "Croque-madame ingredient" , "Quiche ingredient" .)