A bat can fly in total darkness and yet never bump into anything.  The bat has a built-in radar system.  As it flies through the dark, it utters a twittering sound that is too high-pitched for us to hear.  Echoes of these sounds bounce back from any nearby object.

But listening to these echoes with its big ears, the bat is able to avoid obstacles in its path.  The bat also uses echoes to locate the mosquitoes and other insects if catches and eats.  It isn’t true that bats are blind.  They do depend mainly on their keen ears, but most bats can see in daylight. – Dick Rogers