Owl Pellet Studies
PURPOSE AND BACKGROUND
All organisms, whether dead or alive, are potential sources of food for other organisms. The sequence of organisms,
each of which is a source of food for the next, is called a food chain. It determines how energy and nutrients move
from one organism to another through an ecosystem. Because most species participate in several different food
chains, the organisms in most ecosystems form a complex network of interconnected food chains called a food web.
(G. Tyler Miller, Jr., Living in the Environment, 13th ed., Pacific Grove, CA: Brooks/Cole, 2004)
MATERIALS AND EQUIPMENT USED
Probes
Owl pellets
Glue
Gloves
Forceps
Paper
Ruler
Balance
PROCEDURE
Obtain one owl pellet per lab group. Draw a picture of the pellet, and make observations concerning its appearance.
Then, carefully ‘tease’ it open using probes and forceps. Make a stack of any bones you find. Do this until all
bones have been removed from the owl pellets. Glue the bones in some sort of classification pattern (be creative but
realistic) on a piece of construction paper. Make a list of things you can identify and educated guesses on things of
which you’re uncertain. Clean up your mess when finished.
RESULTS
Your results section should include a picture of the owl pellet before beginning and a thorough description of its
appearance, smell, texture, etc. It should include similar descriptions for everything found in it. A data table should
be used to list what you found in the owl pellet and be divided into sections such as bones found or anything else
relevant. Finally, additional pictures should be drawn showing your classification pattern made on your construction
paper and anything else of interest.
Qualitative Data (External Features)
Appearance
Smell
Texture
Drawings
Quantitative Data (Descriptive Stats)
Pellet Mass (g)
Pellet Length (in)
Pellet Width (in)
Total Bone Number
ANALYSIS
Discuss your results in paragraph form, and make sure that you address the following questions:
•
Using the Owl Pellet Bone Chart on the next page, identify as many bones as possible and list them in a
table.
•
On the reverse side of this page, sketch a potential food web that would include an owl, its prey, and at
least 6 other organisms. Then, assuming the owl represents 10 units (mass or energy), sketch and label a
biomass pyramid and energy pyramid that include these organisms.
•
Most of the bones you found probably belonged to voles, mouse-like creatures that live in the Northwest.
Predict what would happen to both the owls and the voles in the following scenarios:
1) A potentially deadly parasite attacks the vole population
2) Foresters in the Northwest put out poison to kill the voles that get into their machinery.
3) Foresters in the Northwest remove the mature trees needed by the owls for nesting.
4) A fungus kills off the timothy grass, a major source of food for the voles.
5) The owls are protected by the Endangered Species Act and multiply in number.
CONCLUSION
• It is a definite controversy in many forests, including the Northwest, about whether or not to protect the
endangered owls. If the owl is protected, foresters will be out of jobs (because the habitat is also
protected). If the owl is not protected, it has a great likelihood of going extinct. What is YOUR opinion on
this controversy? Support your opinion with facts.
SUGGESTIONS FOR FURTHER INVESTIGATION
• What changes would you make to this lab to advance your studies on this subject matter?