Why are BATS mainly nocturnal?? ; Why are these mammals flying like Aves ??

Why are BATS nocturnal, foraging mainly under the darkness of the night ??

Why are they wonderfully winged , with which they fly like Birds instead of four limb appendages to walk on the ground??

Why was their evolutionary sequence , from Aves to Mammals incomplete??

Has thus being an advantage or disadvantage to these flying mammals ?

Would they conclude their evolutionary sequence as Birds in the next centuries ??

How ??