Athene's bird was a Little Owl, (Athene noctua), the Owl was protected and inhabited the Acropolis in great numbers. It was believed that a magical "inner light" gave Owls night vision.
As the symbol of Athene, the Owl was a protector, accompanying Greek armies to war, and providing ornamental inspiration for their daily lives. If an Owl flew over Greek Soldiers before a battle, they took it as a sign of victory.
The Little Owl also kept a watchful eye on Athenian trade and commerce from the reverse side of their coins.