Owl Pellets: Clues from a Hunter's Dinner
1Owls are hunters. They eat mice, voles, shrews, insects and other small animals. An owl often swallows a small animal whole, or in a few large pieces. But an owl cannot digest everything it swallows. Bones, fur and feathers do not break down inside its body. So what happens to them?
2The answer starts in the owl's stomach. Like other birds, an owl has a stomach with two parts. In the first part, digestive juices break down the soft parts of the meal. The leftovers move to the second part, called the gizzard. The gizzard squeezes the fur, bones and other hard parts together into a tight, oval bundle called a pellet.
3Several hours after the meal, the pellet travels back up, and the owl coughs it out of its mouth. An owl usually cannot eat another meal until the pellet comes out, because the pellet blocks the way to its stomach. Owls often return to the same resting spot, called a perch. As a result, pellets can pile up on the ground below it.
4Scientists use pellets to learn what owls eat. Many owls hunt at night, so their meals are hard to watch. Owl stomach juices are not very strong, which means the small bones in a pellet often stay whole. A scientist can match each skull to a mouse, a vole or a shrew. By counting the skulls, the scientist can tell how many animals the owl ate.
5Many students take apart owl pellets in class. First, the pellets are heated so they are free of germs. Next, a student gently pulls a pellet apart with a toothpick or tweezers. Then the student separates the bones from the fur. Finally, the student sorts the bones by shape and uses a bone chart to tell skulls, jaws, ribs and leg bones apart.
6One small gray pellet can tell a big story about where an owl hunts and what animals live nearby.