Although Snowy Owls have few predators, they still have to be watchful of arctic foxes, wolves and other animals during the nesting season. Males defend the nest by standing guard nearby while the female incubates the eggs and broods the young. When a predator approaches both parents will dive-bomb (even wolves!) and try to distract them away from the nest.
During their southern migration we have seen a different kind of predator go after the snowys... crows and ravens. As a Snowy Owl sits, crows and ravens will dive bomb the snowy owl and drop feces on the owl. If enough feces is dropped on the owl, when preening later, the owl digests the toxins and will succumb to the poisoning.