Google says otters will eat ducks but they are not their primary food. Mostly they eat fish but will take a duck if one's available. Will def take ducklings. As for owls, they will eat an entire bird, bones, feathers snd all. And can carry off about 1.5 times its own weight. So yes, a large owl could take a barnyard bird ... so get your ducks in before dusk, when owls start hunting.