Well the house represents yourself, and the bats can represent mystery and unpredictability, being nocturnal and the way the fly around in a random fashion, your unconscious mind may be trying to communicate ideas regarding secrets, which you or someone else prefers to keep hidden. Maybe because you frightened the bats away you would like to be rid of the secrets? This theory could certainly be true as the bats were replaced with birds, creatures that most of us associate with freedom; and the ability to move freely.