The Role of the Owl Pellet in Understanding Food Webs and Biomass Pyramids
Honors Biology
Final Lab!
Introduction:

What is the niche of the barred owl?
Where does it live?
What does it eat?
How are pellets formed?

Diagram a food web (identifying at least one producer, 3 primary consumers, 2 secondary consumers,
1 decomposer, 1 tertiary consumer) in the barred owl’s habitat.
Use the following information to do this:
Prey
Mouse
Mole
Shrew
Rat
Diet
It eats a wide variety of plant and animal matter depending on what is available, including insects and other
vertebrates, seeds, fruits, flowers, nuts, and other plant products. Deer mice sometimes eat their own feces.
A mole’s diet is mostly insects and other invertebrates, including earthworms, centipedes, millipedes, snails,
slugs, grubs, ants, sowbugs, termites, beetles, and crickets.
Food habit studies have revealed that shrews eat beetles, grasshoppers, butterfly, and moth larvae, ichneumonid
wasps, crickets, small snakes, and even other shrews when the opportunity presents itself. Seeds, roots and
other vegetable matter are also eaten by some species of shrews.
The rat’s diet typically includes seeds, nuts, grains, vegetables, fruits, meats, and invertebrates. They consume
about one third of their weight in food every 24 hours. Because of their inability to vomit, rats are very
hesitatnt to try new foods that may be poisonous. They will take a small nibble and wait to see if they feel sick
and if so will avoid that food in the future.
Bird
Insects, terrestrial non-insect arthropods, seeds, grains, and nuts; fruit
 Describe the 10% rule and explain how energy is transferred through an ecosystem.
Hypothesis:
What can be determined from the quantity of prey in the barred owl’s pellet.
If…then…because…what prey would you expect to find the most…why do you know this?
Methods:
Identify the variables:
Types of Variables
Independent variable:
Dependent variable:
Controlled variable (s):
Identify in your dissection
Summarize in a paragraph (past tense, passive voice!) how the procedure was done and how you
systematically determined the prey found within your owl pellet.
Data and Analysis:
Data—Create the following table in your lab notebook
Prey
Length
Number found
Number
Eaten/day
Mouse/Vole
Mole
Shrew
Rat
Bird
XXXXXXX
6.5-9.5
12-14
8
40
15
XXXXXXXX
XXXXXXXXX XXXXXXXX
Number
eaten/week
Number
eaten/year
Total
Analysis—Create a Numbers Pyramid for the owl based on the number eaten per a year with one owl
on the top with the total annual number of all prey below. Use your food web to help you and
assume the owl produces an average of 2.5 pellets/day. Include a trend statement about your
numbers pyramid.
Data—Create the following table in your lab notebook
Prey
Number per
year
Mouse
Mole
Shrew
Rat
Bird
Mass (g) of
organism
(given)
20
55
5
240
20
Mass of
prey (g) in
one pellet
Mass of Prey Kg of prey
(kg)—convert eaten per
from g
day (X2.5)
Kg of prey
eaten per
year (X365)
Analysis—Fill in the table below and then create a biomass pyramid that shows biomass sustaining
one owl for one year. Include a trend statement about your biomass pyramid!
Producer
-After you’ve completed
primary consumers, use
the 10% rule to
determine how many
producers were needed to
sustain the consumers.
Organisms included in
this trophic level:
Primary Consumers
-Add up the biomass per
year for all the organisms
that are primary
consumers.
Secondary Consumers
Top Carnivore (Owl)
-Add up the biomass per -Research the biomass of
year for all the organisms one owl!
that were secondary
consumers.
Organisms included in
this trophic level:
Organisms included in
this trophic level:
Organisms included in
this trophic level:
Biomass in this trophic
level:
Biomass in this trophic
level:
Biomass in this trophic
level:
Biomass in this trophic
level:
Conclusions:
Response to the hypothesis and discussion of data:

Respond to your hypothesis using data from the dissection.

What does the data tell you about the number of mice vs. the number of shrews in the ecosystem?
Why is this?
Connections:
 If an owl could choose to eat whatever it wanted, would it choose to eat a shrew or a mouse?
Explain why in terms of the energy it gets. Apply this to energy you get from different foods in
your diet.

Some owls are endangered. How does a limit in the population of owls affect the ecosystem?

Many scientists strive to preserve biodiversity. Explain how biodiversity is important in terms of
the owl’s diet. In other words, how could the removal of one species from a food web impact
other species in that food web. Use a specific example to explain.
Error:
 Was there variation within the owl pellets seen in this class? If so, how might this have
affected the interpretation of the results or the numbers you used to make your pyramids.

What information might be helpful to better understand your results?

How could we account for differences among individual owls?