OWL PELLET DISSECTION         NAME_________________________

Problem: What does the owl's diet tell us about its habitat? owl screech site

Background Information:   Owl Pellets: When you see an owl pellet, you will think that it is feces, but remember owl pellets are ejected from the mouth.  Owls typically swallow their prey whole or in large pieces.  Owl pellets are masses of bone, teeth, hair, feathers and exoskeletons of various animals eaten by birds of prey (raptors).  Owls feed early in the evening and regurgitate a single pellet approximately 20 hours after eating. Unlike snakes, the protein enzymes and strong acids which occur in the digestive tract of raptors do not digest the entire meal. The relatively weak stomach muscles of the bird form the undigested fur, bones, feather etc. into wet slimy pellets. In this process even the most fragile bones are usually preserved unbroken. A bird's stomach includes an anterior pouch called the proventriculus and a muscular posterior portion called the gizzard. In owls, the gizzard compresses indigestible parts of their prey (hair, bones, teeth, and feathers) into matted pellets. These pellets pass into the proventriculus where they remain until something stimulates the owl to spit them out.  Hawks and other  birds of prey, some gulls and herons also regurgitate undigested remains.  The barn owls produces 1 to 2 pellets per day. 

Scientists study pellets to discover differences in habitat and prey.  Pellets also reveal information about the relative number of small animals found in an owl's feeding area. Pellets are important for scientific study because they give us a picture of what the owl eats.  Other ways to discover what an organism eats is to
    1. Dissect the stomachs of dead animals to see what is found in there.
    2. Examine animal feces to see what plant or animal parts made it all the way through without being digested. (SCATOLOGY)
    
Owl pellets themselves are ecosystems, providing food and shelter for communities which may include clothes moths, carpet beetles and fungi. Clothes moth larvae are frequently abundant in pellets, feeding on fur and feathers. The black spheres about the size of periods (.) that are found in the pellets are the droppings of the caterpillars. The larvae metamorphose near the surface of a pellet in cocoons made of fur. 
    
The pellets WE USE were collected and fumigated to kill all bacteria and parasites. They are perfectly safe to touch.

Materials: owl pellets, probe, used film containers or pill bottles, forceps, old yogurt cups, glue for mounting, paper towel,  identification keys, bone sorting sheet  
(Bone Chart (http://www.carolina.com/owls/guide/Owl_Pellet_Bone_Chart_grid.pdf)

Procedure     fossilized owl pellets BBC

1.Measure the length and width of your owl pellets.

Length of your owl pellet_______

Width of your owl pellet_______

2. Carefully examine the exterior of the pellet. Do you see any signs of fur? __________ 
        Do you see any signs of feathers? ____________

3.  What color was your pellet?  _____________

Put your pellet on a piece of paper towel.  Carefully use a probe to break apart the owl pellet and observe what is in it. Use a probe to expose all bones for identification.  Because some of the bones are so tiny and fragile, if you are not careful, you could either lose or crush a bone.  Use forceps (tweezers) and a probe to do this.  Put the fur aside for disposal.  

Organize the bones into groups (skulls, ribs, vertebrae, leg bones) and label them.  Use the bone diagram to help you identify your bones and assemble the bones on construction paper as shown by the bone sorting chart. Decide how many prey animals you have and record this information on the chart. You may only have one. If more than one, try to sort the bones to go with the skulls.  Glue them to the construction paper.

Next identify your prey animal using the identification guide hung up around the room. Look at the:
    Shape and size of the skull 
    Shape of eye sockets
    Length of the snout compared to the rest of the skull

Grade will be based on neatness, labeling and organization.

Analysis:  Answer the following questions on the back page or on another sheet of paper

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

 6. Owl pellets not only can give us information about the diet of the owl, owl pellets also provide a habitat for other animals, in fact an owl pellet is a little ecosystem all on its own. What kind of animals are found in the owl pellet ecosystem.  (Hint: read the background at the beginning)

 7. Other types of birds form pellets. What would you expect to find in the pellet of a seagull?

 8. Owls, hawks, and eagles are types of raptors, animals which have hooked beaks and sharp claws, and are therefore adapted for seizing prey animals. Hawks and eagles differ from owls in that they eat their prey animals by tearing them into small pieces, picking out the flesh and avoiding most of the fur and bones. They also have strong stomachs which can digest most of the bone material which they might eat. The relatively small amount of indigestible bone and fur that remain will be compacted by their stomach muscles into a pellet similar to the owl's. Do you think an eagle pellet would be as useful for dissecting as an owls? Why or why not?

9. Construct a diagram of a food web (of at least 5 animals) with an owl at the uppermost trophic level. Use an arrow to show which organism is the consumer or predator.

10. How might learning more about the barred owl's diet (what it eats) help us preserve the animal?

11. Based on the data, how would you describe the diet of the owl?

12. What does the data tell us about the habitat of the owl?

13. Based on the information and data in this lab, do you think that we could have owls here in     Brandon?________     Explain your answer.

 bonus question
14.If you were a zoologist doing a study of what deer eat, how would you collect your data?

CONCLUSION: Be sure to summarize what you did 
 

Mouse skeleton

10. Skeleton of LAC Grey mouse.

 


 
BONE SHORTING CHART
rodent bones number

SKULL
 

MANDIBLE

 

SCAPULA
 
                           
HUMEROUS                 RADIUS AND ULNA
Mouse humerus

33. Lateral aspect of right humerus, radius and ulna.

 

 

 

RIBS 
Mouse thoracic vertebra

 

   
Mouse coxae

37. pelvis.

 


PELVIS

   

FEMUR
   

TIBIA AND FIBULA
   

VERTEBRA 

ATLAS

Mouse atlas

AXIS   
 

Mouse axis

18. Axis (2nd cervical vertebra). Left lateral aspect.

 

 
 

   

TAIL BONES
   
                                                            
CARPALS     METACARPALS          TARSALS      METATARSALS
PHALANGES                                                       PHALANGES 
 Mouse pes

44. Upper surface of right pes.

 

   
Rodent Skeleton

LINKS:Life History of the Barred Owl - Ohio DNR    Owl Pellets        Assembling a Skeleton - Virtual Assembly         Owl Digestion    Owl Pages - Barred Owl Natural History        Barred Owl Natural History        USGS Barred Owl Site - w/ Song    Owling.com - World's Largest Owl Website        Owl Images You Can Use