Why are owls considered to be bad omen in indian mythology?
Nope you are misinformed. Owl is not considered as a bad omen because it is thought to be the vehicle of Goddess Laxmi (Goddess of Wealth), who happens to be the wife of Lord Vishnu. As many might be aware Lord Vishnu forms the holy trinity of Hindu Gods along with Lord Shiva and Lord Brahma. So the mode of transportation of the ONLY wife of one of the three major gods can hardly be considered as a bad omen. Also all the pictures of Goddess Laxmi which many Hindus hang on their walls have her owl portrayed on her side.