The owl would be called the predator because it is going after the mice. Therefore, the mice would be called prey. Mice are also nutrients but, nobody uses that word in this situation.
LOL! I'm not taking your question lightly. I think the answer you want is Prey. However, from the Owl's point of view, probably you could answer nutrients. Mice are not predators. Mice are in the middle of the Food Chain. Grass or grains are on the bottom and the Owl is on top.
