Feces turns white most likely due to higher concentrations of calcium in what the animal ate such as bones. Rodent bones in the case of Owls, dog bones in the case of doggie poop in your yard that turn white. And if you are finding white dog poop in your yard is a good indication you need to pick up more often.

Yep, the bacteria gobble up and break down everything else.

Animals eat a lot of bone in their diet. I feed my dogs raw food, and their poop turns white quickly too.

I’ve seen dog poop in a back yard that will turn white if left long enough. So it isn’t just wild animal scat.