Owl Pellet Dissection

Owl pellets are masses of bone, teeth, hair, feathers and exoskeletons of various animals preyed upon by raptors, or birds of prey. The most common prey for owls includes small birds, rodents (mice, voles, shews, rats), and snakes. Owls feed early in the evening and regurgitate a single pellet approximately 20 hours after eating. Therefore, one pellet shows the diet for one days of the owl’s life. These pellets can provide valuable information pertaining to the diet of owls. By studying the contents of owl pellets, one may discover seasonal, regional, and habitat differences and even differences in individual tastes between owls. Also, pellets can be used to effectively illustrate the nature of food chains, to demonstrate the role of avian predators within the ecosystem, and to provide information about the presence and relative abundance of animals in a particular area.

Purpose

1. To successfully extract prey bones from an owl pellet.

2. To explain how pellets are made and how they can be used to do a prey study.

3. To label and arrange bones on a chart.

4. To explain the role of owls in a food web.

Materials

Owl pellets

Dissecting needle/toothpicks and tweezers

Paper

Bone chart and skeleton diagrams

Rubber gloves

Lab Safety: Dispose of your fur and/or feathers and rubber gloves in the trashcan. Clean your work area and wash your hands thoroughly after dissection.

Procedure

1. Place an owl pellet on a white sheet of paper and remove it from its aluminum foil casing.

2. Using your fingers and dissecting needle, carefully separate the bones from the fur of the pellet. Make sure that you get all of the bones, even those that are very tiny. Some of the bones (especially the skulls) will be very fragile.

3. Clean the bones of debris and sort them according to type (for example: skulls, ribs, vertebrae, etc.). Complete Table 1.

Table 1: Owl Pellet Contents

Bone / Number Found / Species
Skull
Jaw
Scapula
Forelimb
Hindlimb
Rib
Vertebrae

4. Determine the number of prey in your pellet (by the number of skulls or jawbone pairs). Use the key to identify your prey animal(s).

Species Number of Individuals

______

______

______

5. Record class findings.

a. What prey animal was represented most often?

b. Of the animals the class found in their pellets, how many different trophic levels are represented? (Please list them.)

Analysis Questions (Please answer on a separate sheet of paper)

1. What do we know about the digestive system of an owl based upon the pellets?

2. Most owls are nocturnal, hunting at night and sleeping during the day. From that information, what can you infer about their prey?

3. Construct a diagram of a food web (of at least 5 animals) with an owl at the uppermost trophic level. Label the trophic levels.

4. In terms of energy flow in an ecosystem, why is the amount of energy passed from one trophic level to the next so small? Since we know energy can’t be destroyed, account for the loss of energy that occurs between the prey and the owl.

Conclusion

Discuss your findings and explain what types of valuable information can be provided by studying an owl pellet. What can we learn about predators and their prey, population sizes, and food chains?