First of all, we would like to say that, if you are looking at having an owl as a pet, you need to do a lot of research first. They are extremely difficult birds to look after, and they need to be working animals, not in a cage in the house. The dietsof an owl are not a simple mix of seeds, pellets, and veg, either, and they would probably not even entertain eating them if you gave them to an owl, either.
As carnivores, owls need to eatmeat, preferably live meat, too. However, as with some other pets, you can not just catch them yourself. You need to buy specialist mice, rabbits, chickens, guinea pigs, etc., from a reputable store or owl food breeder. They are creatures that can cause a lot of damage and mess when they are eating, so there is a requirement to clean up after them, which can be traumatic for some people.