What is incumbent upon one who broke an egg and found in it a chick whose creation was nearing completion, and that was during the day in Ramadan?

The fast is valid in any case. If the matter was unintentional, there is no sin, for Allah Almighty says: "And there is no blame upon you for that in which you have erred, but [only for] what your hearts intended." But if it was intentional, then you should seek Allah's forgiveness, as it involves wasting money.