OWL PELLETS, FOOD WEBS, AND PYRAMIDS
INTRODUCTION
The barred owl inhabits woodlands and swamps in the Eastern part of the United States. This owl is
approximately 43-50 cm long with a wingspan of 99-110 cm and has a mass of about 0.8 kg. Owls are nocturnal
raptors that feed on small mammals, birds, and reptiles. Owls swallow their food whole or if too big may tear it
into chunks. Owls are not able to digest hair, bones, and feathers. The owl digestive system has a specialized
section that presses the undigested portions together forming a pellet. Since the owls cannot pass the pellet
through their digestive system, they must spit out the pellet.
OBJECTIVES
In this experiment, you will
• Dissect and identify the components of an owl pellet.
• Calculate the biomass
• Construct a food diagram (pyramid is a misnomer based on the shape of diagram)
• Estimate over time
MATERIALS
•
•
•
•
•
•
•
•
Owl pellet
Dissecting tools
Cup/Beaker
Water
Butcher Paper (or newspaper)
Identification key (Carolina)
Skeleton diagrams (Carolina)
Sorting sheet (Carolina)
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Carolina Biological Identification Keys and Skeleton Diagrams
http://www.carolina.com/category/teacher+resources/classroom+activities/owl+pellet+interactiv
e+database.do?s_cid=url_owls
PROCEDURE
1. Use gloves, but also wash hands at the end of the procedure.
2. Put pellet in water for about a minute or until you can see it start to loosen. Use
dissecting tools and fingers to gently pry apart the pellet. NOTE: The bones you are
looking for are small and easily broken.
3. Set aside any bones found on separate sheet of paper.
4. Repeat until you have completely dismantled the pellet.
5. Separate the skull bones using the following criteria
a. Shape and size of the skull
b. Shape of eye sockets
c. Length of the snout compared to the rest of the skull
6. Use the identification keys to identify the owl’s prey. Please remember that voles, mice
and rats have similar bones, but there is a huge difference in the sizes (see Table 2 for
masses).
7. Clean up: Wrap ‘waste’ material in newspaper and throw it away; Wash, dry and return
dissection equipment - forceps, probes
PRE LAB
1. Your food chain consists of the following data, calculate the biomass
2. Draw the pyramid of numbers and the Pyramid of Biomass.
Organism
Quantities Average Mass (g) Biomass (kg)
Plant Plankton
1
0.1
Mussel
200
20
Whelk
1000
10
Herring Gull
5,000,000
200
3. Go to :
http://science.malmesbury.wilts.sch.uk/leadictinscience/biology_of_the_seashore.swf
4. Locate a pyramid that is not sustainable. Draw and label it below. Give 2 explanations
about what might occur as a result.
DATA
Fill in Table 1. Use the assumption that an owl produces an average of 2.5 pellets per day.
Please note that a vole is equivalent to a mouse
TABLE 1. Number of Prey eaten by Owl
184
Prey
Number Found
(N)
Number Eaten per Day
(D = 2.5 x N)
Number Eaten per Year
(Y = 365 x D)
Mouse or Vole
Mole
Shrew
Rat
Bird
Total YT =
POST LAB QUESTIONS
1. Create a two-level Numbers Pyramid (from Data Table 1). There will be no
producers in this pyramid.
a.) The top level of the pyramid is the secondary consumer. This equals 1 because
there is only one owl producing the pellet.
b.) The bottom level of the pyramid is the primary consumer. This is the total number
of prey eaten per year (YT)
c.) Make sure to show the correct numerical relationship between top and bottom
level.
d.) Draw the shape that most biology textbooks use to illustrate food pyramids.
2. Draw and fill in Table 2. Note: Number of prey per year (Y) is from Table 1.
Table 2. Biomass of Prey and Producers
Number of
Mass (kg) of
Mass (kg) Mass of Prey (PM =
Biomass of Producers
Prey/year
Producers
(M)
Y x M)
(BM = PM x Prod)
(Y)
eaten by Prey (Prod)
Mouse
0.020
45.6
Mole
0.055
365
Shrew
0.005
1168
Rat
0.240
12.8
Bird
0.020
127
Total PMT
Total Biomass of
(kg)
Producers BMT (kg)
Prey
185
3. Use your calculations from Table 2 to create a three-level Biomass Pyramid
a. The secondary consumer (top-level) is the Barred Owl and its approximate biomass is
indicated in the background information.
b. The biomass of all primary consumers (middle-level) is the Total Mass of the Prey
(PMT).
c. The biomass of all producers (bottom-level) is the Total Biomass of the Producers
(BMT).
4. Does the shape of the pyramid (from question # 8) illustrate the concept of ecological
efficiency of 10%?
Table 3. Owl prey and their respective diet
Prey
Diet
It eats a wide variety of plant and animal matter depending on what is available,
Mouse including insects and other invertebrates, seeds, fruits, flowers, nuts, and other plant
products.
A mole's diet is mostly insects and other invertebrates, including earthworms, centipedes,
Mole
millipedes, snails, slugs, grubs, ants, sowbugs, termites, beetles, and crickets
Food habit studies have revealed that shrews eat beetles, grasshoppers, butterfly and
moth larvae, wasps, crickets, spiders, snails, earthworms, slugs, centipedes, and
Shrew millipedes. Shrews also eat small birds, mice, 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.
Rat Because of their inability to vomit, rats are very hesitant 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
5. Use Table 3 to draw a Food Web that is representative of your pellet. Remember all arrows
go from food to feeder to show the movement of energy.
• Draw and label the owl as the top consumer.
• Draw and label all prey found in the pellet as the next level of consumer (shrew).
• Draw and label any consumers eaten by the prey (crickets eaten by shrew).
• Draw and label any producers eaten by prey or any producers eaten by consumers eaten
by prey (seeds, fruit and grass eaten by crickets; seeds and roots eaten by shrew).
• Draw ‘energy’ arrows from victim towards consumer (head of the arrow points towards
consumer) - From each producer towards each primary consumer that eats that producer.
• Repeat for each level towards the owl. Note: some arrows may be drawn sideways.
6. Why are the arrows pointing toward the top of the food web?
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Post Lab
1. What happens to the number of producers if there is plenty of sunshine and rain?
2. What therefore happens to the number of consumers if there is plenty of sunshine and
rain?
3. What would happen to the number of prey if the owl was removed due to something like
habitat destruction? Why?
4. How would this change the shape of the Numbers Pyramid? Why?
5. How would this change the shape of the Biomass Pyramid? Why?
6. Would this cause the collapse of the food web?
7. If the owl population increases over the next 5 years, what would that do to the food web
you created from Table 2? Specifically mention organisms found in the food web.
8. If the vole was removed from the web because of a pesticide. How would this affect the
rest of the organisms in the web? Be specific and mention trophic levels.
187
TEACHER PAGES
1. There are three types of pyramids that can be drawn: Pyramid of numbers, biomass, and
energy.
Other
Resources
Virtual Owl Pellet Dissection:
http://www.kidwings.com/owlpellets/flash/v4/index.htm
Carolina Biological Identification Keys and Skeleton Diagrams
188
http://www.carolina.com/category/teacher+resources/classroom+activities/owl+pellet+interactiv
e+database.do?s_cid=url_owls
Procedure
8. Use gloves, but also wash hands at the end of the procedure.
9. Put pellet in water for about a minute or until you can see it start to loosen. Use
dissecting tools and fingers to gently pry apart the pellet. NOTE: The bones you are
looking for are small and easily broken.
10. Set aside any bones found on separate sheet of paper.
11. Repeat until you have completely dismantled the pellet.
12. Separate the skull bones using the following criteria
d. Shape and size of the skull
e. Shape of eye sockets
f. Length of the snout compared to the rest of the skull
13. Use the identification keys to identify the owl’s prey. Please remember that voles, mice
and rats have similar bones, but there is a huge difference in the sizes (see Table 2 for
masses).
14. Clean up: Wrap ‘waste’ material in newspaper and throw it away; Wash, dry and return
dissection equipment - forceps, probes
PRE LAB
5. Your food chain consists of the following data, calculate the biomass
6. Draw the pyramid of numbers and the Pyramid of Biomass.
Organism
Quantities Average Mass (g) Biomass (kg)
Plant Plankton
1
0.1
500
Mussel
200
20
20
Whelk
1000
10
2
Herring Gull
5,000,000
200
0.2
7. Go to :
http://science.malmesbury.wilts.sch.uk/leadictinscience/biology_of_the_seashore.swf
8. Locate a
pyramid that is
not
sustainable. Draw
and label it
below. Give 2
explanations
about what might
occur as a
result.
189
There is not enough to eat so the population may eventually die out and animals could go
extinct.
9. What would occur if the plant plankton was removed from the food web? It would
collapse because there would not be enough producers to support the consumers
10. Click on the first food chain circle. Why would this food chain be considered
unsustainable? It is unsustainable because there are a lot more primary consumers than
producers. Therefore, there are not enough producers to supply energy to the upper
levels.
DATA
Fill in Table 1. Use the assumption that an owl produces an average of 2.5 pellets per day.
Please note that a vole is equivalent to a mouse
TABLE 1. Number of Prey eaten by Owl
Prey
Number Found
(N)
Number Eaten per Day
(D = 2.5 x N)
Number Eaten per Year
(Y = 365 x D)
Mouse or Vole
Mole
Shrew
Rat
Bird
14
17
7
0
0
35
42.5
17.5
0
0
Total YT =
12,775
15,512.5
6,387.5
0
0
34,675
POST LAB QUESTIONS
1. Create a two-level Numbers Pyramid (from Data Table 1).
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There will be no producers in this pyramid.
a.) The top level of the pyramid is the secondary consumer. This equals 1 because
there is only one owl producing the pellet.
b.) The bottom level of the pyramid is the primary consumer. This is the total number
of prey eaten per year (YT)
c.) Make sure to show the correct numerical relationship between top and bottom
level.
d.) Draw the shape that most biology textbooks use to illustrate food pyramids.
2. Draw and fill in Table 2. Note: Number of prey per year (Y) is from Table 1.
191
Table 2. Biomass of Prey and Producers
Number of
Mass (kg) of
Mass (kg) Mass of Prey (PM =
Biomass of Producers
Prey Prey/year
Producers
(M)
Y x M)
(BM = PM x Prod)
(Y)
eaten by Prey (Prod)
Mouse 12,775
0.020
255.5
45.6
11650.8
Mole
15,51.5
0.055
853.2
365
311418
Shrew
6,387.5
0.005
31.9
1168
37259.2
Rat
0
0.240
0
12.8
0
Bird
0
0.020
0
127
0
Total PMT
Total Biomass of
1140.6
360,328
(kg)
Producers BMT (kg)
3. Use your calculations from Table 2 to create a three-level Biomass Pyramid
a. The secondary consumer (top-level) is the Barred Owl and its approximate biomass is
indicated in the background information.
b.
c. The biomass of all primary consumers (middle-level) is the Total Mass of the Prey
(PMT).
d. The biomass of all producers (bottom-level) is the Total Biomass of the Producers
(BMT).
4. Does the shape of the pyramid (from question # 8) illustrate the concept of ecological
efficiency of 10%? No, it is less efficient than 10%
Table 3. Owl prey and their respective diet
192
Prey
Diet
It eats a wide variety of plant and animal matter depending on what is available,
Mouse including insects and other invertebrates, seeds, fruits, flowers, nuts, and other plant
products.
A mole's diet is mostly insects and other invertebrates, including earthworms, centipedes,
Mole
millipedes, snails, slugs, grubs, ants, sowbugs, termites, beetles, and crickets
Food habit studies have revealed that shrews eat beetles, grasshoppers, butterfly and
moth larvae, wasps, crickets, spiders, snails, earthworms, slugs, centipedes, and
Shrew millipedes. Shrews also eat small birds, mice, 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.
Rat Because of their inability to vomit, rats are very hesitant 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
5. Use Table 3 to draw a Food Web that is representative of your pellet. Remember all arrows
go from food to feeder to show the movement of energy.
• Draw and label the owl as the top consumer.
• Draw and label all prey found in the pellet as the next level of consumer (shrew).
• Draw and label any consumers eaten by the prey (crickets eaten by shrew).
• Draw and label any producers eaten by prey or any producers eaten by consumers eaten
by prey (seeds, fruit and grass eaten by crickets; seeds and roots eaten by shrew).
• Draw ‘energy’ arrows from victim towards consumer (head of the arrow points towards
consumer) - From each producer towards each primary consumer that eats that producer.
• Repeat for each level towards the owl. Note: some arrows may be drawn sideways.
193
6. Why are the arrows pointing toward the top of the food web? The consumers are eating the
food level below them therefore they are getting the energy.
Post Lab
1. What happens to the number of producers if there is plenty of sunshine and rain? The
amount and biomass of producers increases.
2. What therefore happens to the number of consumers if there is plenty of sunshine and
rain? Therefore, the amount and biomass of consumers increases.
3. What would happen to the number of prey if the owl was removed due to something
like habitat destruction? Why? The prey would increase exponentially. If they had no
natural predators to control the population, then it would grow rapidly.
4. How would this change the shape of the Numbers Pyramid? Why? The secondary
consumer level would be nonexistent and the primary consumer level would be much
thicker. If there are no secondary consumers to eat the primary consumers, then their
numbers will increase.
5. How would this change the shape of the Biomass Pyramid? Why? The secondary
consumer level would be nonexistent, the primary consumer level would be much
194
thicker, and the producer level would decrease considerably. If the primary consumer
levels increase, then there will be more consumers that eat the producers, causing the
biomass of the producers to decrease.
6. Would this cause the collapse of the food web? Yes, it would. There may not be
enough producers to support the consumption rate of the primary consumers.
7. If the owl population increases over the next 5 years, what would that do to the food
web you created from Table 2? Specifically mention organisms found in the food
web. The food web would collapse. The owls would over eat and the bird, mouse,
shrew, rat, and vole and their population would decrease. Therefore, the plant
biomass would thrive in over abundance.
8. If the vole was removed from the web because of a pesticide. How would this affect
the rest of the organisms in the web? Be specific and mention trophic levels. The owl
population would decrease because of lack of food. Therefore, the other primary
producers would thrive and the producers would decrease do to overeating.
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AP* Environmental Science:
Name: ______________________________
Period:_____________
Directions: Answer the question; the suggested time is about 22 minutes for answering this question. Write all
your answers on the lines following the question and not on a separate piece of paper. Where calculations are
required, clearly show how you arrived at your answer. Where explanation or discussion is required, support your
answers with relevant information and/or specific examples.
Species such as the dusky seaside sparrow, the passenger pigeon, and the woolly mammoth are extinct.
Populations of other species have declined to the point where they are designated as threatened or endangered.
(a) Identify one threatened or endangered species and explain why its population has declined.
(b) Describe three characteristics of organisms that would make them particularly vulnerable to extinction.
(c) Present three arguments in favor of the maintenance of biodiversity.
(d) Name and describe one United States federal law or one international treaty that is intended to prevent
the extinction of species.
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(1) Test Questions are Copyright © 1984-2002 by College Entrance Examination Board, Princeton, NJ. All rights reserved. For face-to-face teaching purposes, classroom teachers are permitted to reproduce the
questions. Web or Mass distribution prohibited. (2) AP® is a registered trademark of the College Entrance Examination Board. The College Entrance Examination Board was not involved in the production of
and does not endorse this product. Permission is granted for individual classroom teachers to reproduce the activity sheets and illustrations for their own classroom use. Any other type of reproduction of these
materials is strictly prohibited.
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AP* Environmental Science
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Period:_____________
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AP* Environmental Science
Name: ______________________________
Period:_____________
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2000 AP® ENVIRONMENTAL SCIENCE FREE-RESPONSE QUESTIONS
3. Species such as the dusky seaside sparrow, the passenger pigeon, and the woolly mammoth are extinct.
Populations of other species have declined to the point where they are designated as threatened or endangered.
(a) Identify one threatened or endangered species and explain why its population has declined.
(b) Describe three characteristics of organisms that would make them particularly vulnerable to extinction.
(c) Present three arguments in favor of the maintenance of biodiversity.
(d) Name and describe one United States federal law or one international treaty that is intended to prevent the
extinction of species.
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AP is a registered trademark of the College Entrance Examination Board.
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AP® Environmental Science 2000 ─ Scoring Standards
Question 3 Scoring Guide
(a)
2 POINTS MAXIMUM
1 point earned for identification of a specific species. General names are not accepted (e.g., whale,
owl), unless all members of the group are endangered (e.g., elephant).
Examples of Species Accepted
Giant panda, elephant, whooping crane, manatee, rhinoceros, California condor, bald eagle,
western lily, wooly spider monkey, Florida panther, blue whale, Galapagos tortoise
1 point earned for explanation linked to species above
Examples of Explanations Accepted
● habitat alteration for a specific reason, such as:
- human encroachment (urban sprawl)
- fragmentation (building highways)
- conversion (building a marina)
- simplification (agriculture)
OR
- identification of the specific habitat altered (e.g., “The bamboo forest needed by the
giant panda has been destroyed.”)
● hunting or poaching for a specific reason (e.g., food, sport, commercial, cultural beliefs)
● inability to compete with non-native or invasive species (must be specific,
e.g., “Arrowroot is outcompeted by the non-native purple loosestrife.”)
● pollution (must be specific, e.g., “Lead poisoning of bottom-feeding waterfowl.”
● pest control (must be specific, e.g., “DDT causes thin egg shells in bald eagles.”)
(b)
3 POINTS MAXIMUM
Each characteristic must be clearly described, explained, or a specific example must be provided
(only first three are graded)
Acceptable characteristics (need description)
- specialized feeding behavior/food source
- requires large territory
- preys on livestock/people
- competition with humans (for space/food)
- no natural defense (against introduced species)
- fixed migratory patterns
- specialized reproductive behavior, breeding
- low reproductive rate
- limited geographic range, habitat
- specific behavior patterns
- exploited for economic value (specific)
- k-strategist
- feed at high trophic level, biomagnification
- large size
- slow speed
- limited range of tolerance
- small population linked to lack of genetic diversity
Copyright © 2000 College Entrance Examination Board and Educational Testing Service. All rights reserved.205
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AP® Environmental Science 2000 ─ Scoring Standards
(c)
3 POINTS MAXIMUM
1 point earned for each argument (only first three are graded)
● ecosystem function and/or stability based on a specific reason such as
- organism's role in food web (e.g., keystone species, predator-prey relationships)
- organism's role as a pollinator
- organism's role in nutrient cycles (e.g., decomposer, nitrogen-fixer)
● future medical resources
● future food resources
● economic potential (ecotourism, future products with market value)
● genetic bank (species diversity to allow continued evolution)
● recreation (hiking, camping, hunting, fishing, etc.)
● scientific value for research/natural lab
● scenic/aesthetic value
● symbolic/religious value
● intrinsic value/ethical reasons (organism have inherent right to live, ecological wealth)
● provides resources for indigenous human population
● minimizes spread of infectious diseases
(d)
2 POINTS MAXIMUM
1 point earned for naming the law or treaty
1 point earned for describing the law
Federal Laws (1 point)
Endangered Species Act
(ESA)
Components (1 point; need ONE of the following)
- identify species that are endangered/threatened or
- protect endangered species from one of the following:
import/export, taking, harassing, harming, hunting, shooting,
wounding, trapping, killing, capturing, collecting, possessing,
selling, delivering, transporting, shipping, receiving or
- penalize violators or
- design protection plans or
- reintroduce species or
- protect habitat
Lacey Act - prohibits transport of protected species between states
The following are also acceptable with a correct description:
Wild Bird Conservation Act
Eagle Protection Act
Migratory Bird Treaty Act
African Elephant Conservation Act
Whaling Conservation and Protection Study/Act
Fur Seal Act
Marine Mammal Protection Act
Whaling Convention Act
Migratory Bird Conservation Act
Fish and Wildlife Conservation Act
Fish and Wildlife Coordination Act
Fish and Game Sanctuary Act
Marine Protection, Research and Sanctuary Act
Fish and Wildlife Act
Wildlife Restoration Act of 1937 (Pittman-Robertson Act)
National Wildlife Refuge System Administration Act
International Treaties:
● CITES (Convention on International Trade in Endangered Species) – regulates international trade
of protected species and their products
● Convention on Biological Diversity – treaty signatories are expected to adopt biodiversity plans,
establish protected ecosystems, promote sustainable use of biological resources, restore degraded
habitats, protect threatened species
● International Whaling Commission Ban on Whaling – imposed moratorium on whaling
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207
208
209
AP® ENVIRONMENTAL SCIENCE
2000 SCORING COMMENTARY
Question 3
Sample Q – Score 10
This student gave a thorough answer that was typical of students who scored highly on the
question. An endangered species (giant panda) was identified and a reason for its declining
population given. Three characteristics that would make a species vulnerable to extinction were
cited and clearly explained. The student presented three sound arguments for maintaining
biodiversity, before going on to name and describe the Endangered Species Act.
Sample R – Score 8
This student did not correctly identify an endangered species, but scored the maximum number
of points in the other sections. Well-explained examples were given in part (b), and concise
arguments made in part (c). The Endangered Species Act was named and described in part (d).
Sample S – Score 6
The manatee was named as the endangered species and a reason for its decline stated. The
student scored full points in part (b), did not any receive credit for part (c), and was awarded one
point for naming the Endangered Species Act.
Question 4
Sample Q – Score 10
The student gave a well thought out answer, representative of those receiving a high score on this
question. The countries with the largest and smallest rates of population growth were correctly
identified and explained. A sound comparison and reasoning for the difference in infant mortality
between Countries X and Y was given in part (b). The description of the demographic transition
was concise and showed a high degree of clarity, scoring maximum points for part (c). In part
(d), an incentive was stated and a linked drawback to the incentive was described, allowing the
student to receive one point for each.
Sample R – Score 8
The student received the maximum number of points in parts (a) and (b), but only attained one
point in part (c) for stating that both the birth and death rates decrease as a country becomes
industrialized. One point was given for naming an incentive and a further point was attained for a
linked drawback in part (d).
Sample S – Score 6
This paper is a good example of a student answer that scored in the mid-range for this question.
The student correctly identified Country X as having the largest and Country Y as having the
smallest rate of population growth, receiving one point for each answer. No credit was given for
part (b). One point was awarded in part (c) for stating that both the birth and death rates decrease
as a country becomes industrialized. In part (d), the student scored the maximum number of
points for naming an incentive, explaining how it would work, and describing a drawback which
was linked to the incentive.
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