Why are owl pellets important for scientists to study?

Owl pellets are very important for scientists because when they study the components of the ball of pellet they find the bones of the animals that the owl has eaten, mostly small rodent and bats, so he can know what kind of small mouse and bat live in the area. If the scientist takes up the pellets of the owl regularly, then he can observe the variations of these populations: the growth or diminution of the populations of mice and bats is showed by the augmentation or diminution of the bones in the owl's pellets.