The Wild Mammals of Missouri is a good reference for identifying rodents from skulls and other fragments. Look for it in a school or public library. Great horned owls usually eat mice, voles, shrews and rabbits, but sometimes they eat skunks, muskrats, house cats, weasels, mink, flying squirrels, snakes, frogs and birds. They will even attack and eat other hawks and owls. Predators, such as owls, are an important part of nature.
Owls survive by eating the large number of mice and other animals produced by nature each year.
By consuming this surplus, owls help to control some prey populations. This codependency brings about a balance between predator and prey.