Experiment 4: Owl Pellet Dissection

Birds of prey often consume their prey whole rather than selecting the digestible components. However, proteolytic enzymes present in the bird’s stomach are not capable of digesting different structures in an organism and often cannot break down hair, teeth, bones, or exoskeletons. As a result, owls (like many other predatory bird species) produce and regurgitate pellets that contain many of these undigestible items approximately 18 - 20 hours after to consumption. Very small bones or bone fragments occasionally pass through the pyloric sphincter and proceed through the digestive system, but pellets often contain complete animal skeletons.

In this experiment, you will probe a barn owl (Tyto alba) pellet to learn more about the skeletal system’s general physical characteristics. Note that some of the bones that you recover from the pellet will appear homologous to a human skeleton (e.g., the ribs and vertebra), while others will vary significantly (e.g., the skull).

Caution: The owl pellets have been heat-treated but may still harbor microbes. Wear protective glasses, gloves, and apron when performing this experiment. Thoroughly wash your hands and all work surfaces with warm water and soap after you finish.

Procedure

1. With your gloves on, unwrap the aluminum foil and set the owl pellet on the black construction paper. This will make it easier to identify the bones in the pellet as you dissect.
2. Measure in centimeters the dimensions of your pellet. Record your data in Table 3.
3. Review the physical characteristics of the pellet such as texture, color, scent, etc. Be sure to use the wafting technique to detect the scent of the pellet (see the Appendix for a description of this technique). Record your observations in Table 3.
4. Carefully use the toothpicks and forceps to probe the pellet. If your pellet feels very firm, submerge it in a beaker filled with water for 1 - 3 minutes to soften it.
5. Isolate any bones you come across.
6. Continue to probe the pellet for bones, removing fur and debris from the bones. Note that the bones will be fragile. Be careful not to break any of the bones during the dissection.
7. Use Figure 15 to identify the bones found in the pellet. Record the bones you identify in Table 3.
8. Try to re-create the skeleton of one animal found in the pellet by organizing the bones in the arrangement of the skeletal system. Pay particular attention to where the joints might have been located.
   Note: Each pellet is likely to contain bones from several different animal species. Be sure to refer to Figure 15 to complete this step.
9. Dispose of the pellet in a trash receptacle that is safe from the reach of children or animals. Then, wash your work station with warm water and soap.

Figure 15: Owl pellet bone identification chart.