The Owl, or the Uluka in Sanskrit, is Devi Lakshmi's vahana (vehicle); In Sanskrit, Uluka stands for an owl. Uluka is also one of the names of lndra, the king of gods, personifying wealth, power and glory. Thus, Lakshmi, the goddess of fortune, could not have found a better person to ride on than the king of gods.
The owl is a bird that sleeps through the day and prowls through the night, and though this bird appears to be the unlikeliest vehicle for the lovely Goddess, there is a deep spiritual significance as to why she selected this creature as her mount.
This is because it can only see in the dark and goes blind in the day. This partial blindness in the creature is actually indicative of a sadhaka's (seeker) tendency of going toward the pursuit of secular instead of spiritual wealth. Her vehicle white owl takes her to the darker areas so that they can be enlightened and can be removed darkness of poverty, anger, laziness from her devotee’s lives.
It is believed that goddess Lakshmi visits only those houses which are clean; where the people are hardworking and sincere about their wealth. And that is why people who wish to acquire or to preserve wealth worship goddess Lakshmi.
The owl, in the Bhagavad Gita, is likened to an enlightened sthita prajna (the one who remains unwavering to any situation, whether it is happy or sad). Goddess Lakshmi is also said to be the mistress of spiritual wisdom. By keeping the owl as her vehicle, she teaches us to open our eyes to the light of the wisdom residing within us. This Karunamayi (Compassionate One) Mother, hence, symbolically keeps ignorance under her control.
Another interpretation is “Shut not thy eyes to the light of wisdom from the Sun of knowledge”. Out of consideration for mankind, the all compassionate mother has kept this personification of ignorance under her control.
In Orissa and Bengal, Lakshmi images include a white owl. In local belief, white owls have come to be associated with auspiciousness and good luck because of their association with the goddess.
Some say, Lakshmi rides the owl; others believe the owl simply accompanies her while she rides on a elephant, the latter being a more appropriate vehicle for the goddess who is associated with wealth, power, and royal splendor.
Because of the owl’s round eyes that never move and stare straight ahead, it has been associated with wisdom in many parts of the world, especially ancient Greece, where it was closely associated with Athena, goddess of wisdom.
The term "lord with circular eyes" (Choka-dola) is used in the East to refer to Jagannath, the form of Krishna-Vishnu worshipped in Puri, Orissa, leading to speculation that the owl actually represents Lakshmi's consort, Vishnu.
(sources: http://in.answers.yahoo.com/question/index?qid=20100226084244AA6Nvyx and http://www.mid-day.com/specials/2009/may/030509-Alakshmi-goddess-of-strife-Lakshmi-twin-sister-Indian-Mythology-Owl-Devlok.htm and http://mogulinterior.blogspot.com/2008/11/lakshmi.html)