Why are owls considered wise?

People have associated owls with wisdom since before recorded history.  Curiously, this belief evolved separately in several different cultures.

Owls, as night birds, are shrouded in mystery and are apt to become depositories for superstitions, just as nightjars and bats have.  Most of the original beliefs linked owls to evil-- over time the beliefs evolved and it became a foreteller of death, a bringer of ill omens, a bird of prophecy, and finally achieved a connotation with wisdom.

There are a few other odds and ends that may have helped the symbolism--

• The goddess Athena controlled wisdom and darkness- her symbol was the owl.
• Owls have extremely large eyes, which could make them seem "all-seeing"
• Owls come and go mysteriously-- their ways were largely unknown to humans up until the last couple of centuries.  It may have been assumed that because of this owls possessed some kind of knowledge we did not.
• Darkness blinds humans, but it is the owl's element-- this also may have made them seem to be knowing something we don't.
• Early Christian texts used the owl as a metaphor for Jesus, who appeared in the darkness of sin and showed humans the way to salvation.

It's also important to realize that not all cultures connect owls with wisdom.  For many African cultures, the owl is nothing but evil; early European cultures viewed the owl as somewhat foolish, and some Native American tribes used the owl as a symbol of bravery or protection from evil.