Grade 9 Academic Science – Unit Sustainable Ecosystems
Transfer of Energy – Owl Pellet Dissection
Laboratory Assignment
Section 2.7 Page 52-55
Introduction
We have learned that every organism within an ecosystem provides energy for other
organisms. We show this transfer of energy by drawing a food chain. From a food chain, we
know the following features:
1. Producers (i.e., plants, algae and some bacteria) make their own food from nutrients
and sunlight,
2. Primary consumers feed directly on producers to obtain energy, and
3. The next trophic level in a food chain relies on the previous level for energy (e.g.,
secondary consumers eat primary consumers).
We also know that some of the energy changes form as it is transferred within an
ecosystem. Moreover, not all the energy in lower trophic level is transferred to the next trophic
level. Some of the energy is used for living (e.g., staying warm, breathing, moving, growing).
Energy used for living cannot be transferred to the next trophic level. This is called the Rule of
Tens: only 10% of the energy in one trophic level is transferred to the next level.
This transfer of energy (…or lack of…) can be illustrated by examining owl pellets. When
an owl (or another large bird of prey such as a hawk or eagle) consumes its prey, not all parts of
the prey are digested. The soft parts of the prey (e.g., tissue, organs) are dissolved. However,
the hard parts remain intact, and since the owl cannot use bones, teeth, hair, fur, feathers, scales
or insect skeletons, these parts are regurgitated to form the basis of an owl pellet.
These pellets are from barn owls, Tyto alba. A barn owl feeds early in the evening. A
single pellet is regurgitated 18-20 hours after feeding.
From pellet dissection, scientists have estimated that an adult owl required 80-100 grams
of prey each day.
Owl pellets are masses of bone, teeth, hair, feathers and exoskeletons of various animals
preyed upon by raptors, or birds of prey. Pellets are produced and regurgitated not only by owls,
but by hawks, eagles and other raptors that swallow their prey whole of in small pieces. 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.
The owl pellets that you will be examining in this lab have been collected and fumigated.
There is minimal risk to you.
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.
Transfer of Energy – Owl Pellet Dissection - Laboratory Instructions (Dissection)
1. Measure and record the length and width of your pellet in millimeters (mm).
2. Using a weigh scale, determine and record the total mass of the pellet in grams.
3. Open your pellet and remove all intact and undigested pieces (e.g., bones, feathers, fur).
Using the weigh scale, determine and record the total mass in grams of all intact and
undigested pieces.
4. Using the attached skeletal chart, identify the undigested parts. Attach the parts to the
skeletal chart. Record the bones you uncover during your dissection in the following
table. NOTE: You may only be able to identify skulls and jaw bones for more than one
prey.
BONE
ORGANISM TYPE
NUMBER
Skull
Jaw
Scapula
Forelimb
Hind Limb
Pelvic Bone
Rib
Vertebrate
Other
5. It is not enough to simply know how many of each prey type that the owl eats because
the animals are different sizes. The owl might have eaten a greater number of mice than
rats, but because the rat is so much larger, the owl might have received greater
nutritional value (e.g., gotten more "food") from the rats. NOTE: If you had three
hamburgers for lunch and 10 French fries (single pieces), you would probably feel
stuffed, but it would be the hamburgers that filled you and not fries.
When we calculate the biomass for each prey, we are taking into account the weight of
the prey. We get biomass units by multiplying the number of each animal by a
conversion factor that is based on the weight. An example of an owl eating four mice
and one is attached.
Complete the table from your findings
Prey
Mean Mass
Conversion Frequency
Factor
(g)
Vole
2
Mouse
1
Mole
2.75
Shrew
0.25
Rat
12
Bird
2
Percent of
Diet
Biomass
Unit
Percent of
Biomass
Using the data for Percent Biomass, construct a pie chart for each species of prey. We
use a circle graph whenever we have parts of a whole. All the biomass percentages add
up to a whole (100%), the total diet.
6. Examine four other team results, and record their information including
 mass and size of pellet
 number of prey inside each pellet
 percent of biomass of each prey
Team 1
Team 2
Team 3
Team 4
7. Using the class information, make a FREQUENCY DISTRIBUTION GRAPH for (i) Pellet
size and (ii) Number of Prey.
8. Answer the attached questions.
9. Draw a food web for the barn owl with the barn owl as the top predator.
10. Submit your information, answers to the Discussion Questions, skeletal chart and a
completed laboratory report for marking.
Laboratory Discussion Questions
1. What kind of animals were the most important food sources for these owls?
2. What was the average number of skulls found in each pellet? Use information from five
groups to calculate an average.
3. If an owl produces one pellet per day, how many small animals does one owl consume in
one year?
4. What is a possible niche for barn owls?
5. If a farmer studied the results of your owl pellet research, would the farmer consider the
owls helpful of harmful to the farming operation? Give one reason for your answer.
6. How might the field ecosystem near the farm change if the farmer killed the barn owls?
Provide two changes you would expect.
7. Wheat is a major farming crop. The farmer learns that more bushels of wheat were
harvested after the owls came to habitat the barn. In what way were the owls responsible
for the larger wheat harvest? Provide one idea as your answer.
8. The farmer decides to spray an organophosphate pesticide on the field. What could
happen to the ecosystem? Provide two ideas.
9. Draw a simple diagram to show how the owl pellet represents a separate ecosystem
10. Does an owl pellet give up a good indication of the number of small mammal species
living in the field ecosystem? Provide two ideas with your reason.
Discussion Questions Total Marks ______________ / 15 marks
Transfer of Energy – Owl Pellet Dissection
Identification Key
Simplified Key to Mammal Skulls that maybe found in an Owl Pellet
1.
(a) Teeth are present or missing but tooth socket is present, eye socket is
not completely surrounded by ridge or bone, bones are
thick…………………………………………………Mammal….Go to 2
(b) No teeth or tooth sockets are present, eye socket is surrounded by a
ridge of bone, bones are thin………………………………………Bird
2.
(a) There is a wide space between the incisors and the molars…..Go to 4
(b) Teeth form a continuous row………………………………………Go to 3
3.
(a) Skull <28 mm, teeth red or dark red in colour, cheek bone does not
form a ridge which meets the upper jaw bone…………………Shrew
(b) Skull >28 mm, teeth white or gray, cheek bone forms a ridge where it
meets the upper jaw bone………………………………………..Mole
4.
(a) Two incisors on the upper jaw…………………………………….Go to 5
(b) Four incisors on the upper jaw…………………………….Rabbit or Hare
5.
(a) Teeth are flat and form a series of loops or triangles…………..Go to 6
(b) Teeth are not flat and do not form a pattern of loops or triangles………
……………………………………………………………………Go to 9
6.
(a) Upper teeth have a lengthwise groove on front outside edge …………..
………………………………………………..Southern Bog Lemming
(b) Upper teeth do not have a lengthwise groove……………………Go to 7
7.
(a) Skull length is 50 mm or greater…………………………………..Muskrat
(b) Skull length is less than 50 mm………………………………........Go to 8
8.
(a) Skull length is 45-49 mm. ……………………………..Eastern Wood Rat
(b) Skull length is less than 45 mm……………………………….............Vole
9.
(a) Skull length is less than 25 mm……………………………............Mouse
(b) Skull length is more than 25 mm……………………………………….Rat
Barn Owl

On the internet go to the following website http://www.sararegistry.gc.ca to answer the
questions:

Search for ‘barn owl’
1. Is this species a producer, consumer, scavenger or decomposer? _______________
2. (a) Is this species classified as endangered, threatened, extirpated or extinct?
_________________________
(b) In your own words, what does this classification mean?
_______________________________________________________________
3. Describe this species
4. Describe the habitat of this bird
5. What were the main threats to the species?
6. Is there any recovery in the population over the last few years? If so, describe what has
been done to help.