Bats never see day and night. Bats actually make their way through sound waves. As the bat moves, it spreads a kind of sound wave in the air. That sound is reflected in the house , the trees , the mountains or any big obstacle and comes back to the ears of the bats. In this way they find the right direction to walk. The bat's brain can tell by the reflected sound how far the front barrier is. But most of the world's animals, including humans, stay awake during the day. Millions of words are spread in the air because of their daily activities. That special sound wave of the bat's path is lost in the noise of the daytime animals. So the bat does not leave its nest during the day because it cannot find its own sound wave in the crowd of billions of sound waves.