The owl is often depicted alone and symbolizes wisdom and education. It's an element present in the iconography of many past civilizations, from the ancient Hindus, to the Egyptians to arrive at the Celts, who believed it was the protector and guardian of the dead.
Hence the name angel of death as it is commonly called. The owl is also found in Greek culture, such as the animal very dear to the goddess Athena (goddess of learning). To the Native Americans, instead, the owl was the bearer of the sacred knowledge.