What animals are natural predators of the burrowing owl?

Ravens are very intelligent birds, and will eat just about anything, depending upon their circumstances and what's available. However, In North America, Ravens are most commonly known as scavengers, meaning they spend a lot of time on and around other dead animals. As a result, it is not unusual for them to be attacked and killed at carcasses by other predatory animals, such as coyotes and bobcats. I'm not aware of any other animals that actively hunt down and kill ravens, however, it is conceivable that some large Birds of Prey such as hawks and owls could prey on them on occaision. Great Horned owls have been known to kill ravens (and other birds) as they roost at night, but it is not very common. Skunks, raccoons, and various types of snakes will invade the nests of ravens and eat their eggs and young, and Magpies have been known to do the same.