In winter, we have much snow in Nagano. So it is hard to go to the mountain to observe owls and set traps for owls preys. But we can study about owls and their preys. We look into owls which were killed by accidents. We want to conserve owls so we have to know owls. We analyzed owls pellets to learn what they ate. If we can find prey’s skull, it give us identify them.