Name: _____________________________________________ Date:_________ period:_____
Unit 4: Ecological Interactions
Owl Pellet Lab
Essential Question: How does energy flow through the ecosystem?
INTRODUCTION
Owl pellets are the remains of prey eaten by an owl that they could not
digest. The owl swallows its prey whole, and during the process of
digestion, the soft parts of the prey are broken down and passed on to
the intestines where nutrients can be absorbed into its body. The hard,
non-digestible parts - bones, teeth, fur, feathers, etc. - are compacted in
the gizzard and passed on to the first chamber of the owl’s stomach
(proventriculus), where the pellet remains until it is vomited by the
owl.
Pellets are not only made within owl families. There are many species
of birds known to vomit pellets: hawks, eagles, kites, harriers, falcons, and even robins are some of the more
familiar ones.
The Common Barn Owl feeds in early morning and early evening and will usually produce one to two pellets
per day. Glossy black when fresh, the pellet remains smooth and dark in color when dry. Each pellet has
been cleaned to rid it of any insects and then individually wrapped for preservation. Unless otherwise stated,
the pellets in this lab are from Common Barn Owl. Watch the following clip to see exactly how owl pellets
are prepared so you can dissect them, http://www.discovery.com/tv-shows/dirty-jobs/videos/owl-vomitcollector.htm .
INTRODUCTION
SAFETY
1. Be careful, teasing needles are very sharp. They are not toys.
2. Wash hands before leaving the lab.
MATERIALS
owl pellet
2 teasing needles
forceps
dissecting tray
hand lens
(diluted bleach)
bone sorting charts
foil
calculator
PROCEDURE
Part 1: Pellet dissection
1. Work in pairs as directed by the teacher.
2. Remove the pellet from the aluminum foil.
3. Place the pellet in your dissecting tray. Carefully separate the bones from dried fur or feathers using a
teasing needle and forceps.
4. Carefully clean the bones and sort them according to type, skulls, jaws, vertebrae, etc.
5. When you are sure that all bones have been removed from the fur, you may discard the fur and/or
feathers.
6. Identify the number and types of animals found in your pellet by comparing your skulls to the skulls in
the picture keys. Record your data in Table 1 and on the chart in the front of the room.
8. When the last group has recorded their data on the board, copy the class data in column C in Table 2.
DATA
Table 1. Kinds and Numbers of Animals Found in Individual Owl Pellets
Vole
Shrew
Bird
Mouse
My Data
Mole
Rat
Table 2. Numbers and Biomass Data table
A
B
PREY
TYPES
Biomass
Mouse
20 g.
Rat
240 g.
Bird
80 g.
Shrew
5 g.
Vole
40 g.
Mole
76 g.
Total
C
Total
number
found by
class
D
=
C/# of class
grps
E
F
G
H
=
D x 365
=
BxD
=
F x 365
=
G x 2.5
Average
number found
per pellet for
class
Average
number eaten
per year (1
pellet per
day:365
days)
Average
biomass
eaten per
day(g)
Average
biomass
eaten per
year (365
days) (g)
Average
biomass
eaten over a
2.5 year
lifespan (g)
X
X
X
X
Use this # to
calculate R for
Number Pyramid
Use this # to
calculate R for
Biomass Pyramid
Part 2: Food Chains and Food Webs
In every ecosystem, primary producers and consumers are linked through feeding relationships. Even though
these feeding relationships differ, energy always flows from the primary producer (autotroph) to the
consumers. Scientists can illustrate these feeding relationships and the flow of energy using food chains and
food webs.
A food chain is a series of steps in which organisms transfer energy by eating and being eaten. Since many
organisms eat more than one kind of food, food webs are used to show this network of feeding relationships.
In both food chains and food webs, the tip of the arrow always points in the direction the energy is flowing
to.
Directions:
Step 1: Use the images provided and the information
below to construct a complex food web by drawing
arrows to show the flow of energy.
o OWL EATS: Field Mouse, Vole, Bird, Shrew,
Mole, Lizard, Grasshopper, Beetle, Moth
o FIELD MOUSE EATS: Grass and Seeds,
Grasshopper, Beetle, Moth
o VOLE EATS: Plant Roots, Grass and Seeds,
Grasshopper, Beetle, Moth
o BIRD EATS: Seeds, Grasshopper, Beetle, Moth
o SHREW EATS: Grasshopper, Beetle, Moth
o MOLE EATS: Grasshopper, Beetle, Moth
o LIZARD EATS: Flowers, Seeds, Grasshopper,
Beetle, Moth
o GRASSHOPPER EATS: Leaves, Grass, Seeds
o BEETLE EATS: Leaves, Flowers, Seeds
o MOTH EATS: Flowers
Step 2: In your food web above
(A) Circle all the producers,
(B) Box all the Herbivores,
(C) Star all Omnivore and
(D) Put an “X” by all carnivores
Part 3: Ecological Pyramids
The amount of energy or matter in an ecosystem can be illustrated by a drawing called an ecological
pyramid. In this activity you will construct three types of ecological pyramids: (1) a number pyramid, (2) a
biomass pyramid and (3) an energy pyramid.
Each pyramid you construct will consist of four trophic levels, or steps in a food web/chain. The top of each
will relate to your owl, the only tertiary(third-level) consumer (3°). The next level down will relate to the
owl’s prey, the secondary (second-level) consumers (2°). For the purposes of this activity, assume that all
of the prey found in the owl pellets are secondary consumers. The next trophic level down will relate to the
organisms eaten by the owl’s prey, the primary (firstlevel) consumers, (1°). The base of each pyramid will
relate to the organisms eaten by the primary consumers,
Owl
the producers.
Directions: Describe the organisms in each trophic level
according to the passage above and record it in the
pyramid. The first one is done for you as an example.
Directions: Use the information obtained from your owl pellet dissection to construct the ecological
pyramids below.
Number Pyramid (For 1 Week )
A number pyramid is an ecological pyramid that shows the total number of organisms in each trophic level
There is only 1 owl, which is the 3° consumer and it is labeled for you. On your data table (column C, total),
you have calculated the total number of prey found in each pellet for your class, this will be the number of 2°
consumers and your “R” value.
1. Multiply each trophic level by R to get the total number of each type of organism consumed at each
trophic level. Record it in the pyramid below.
Number Pyramid
(Fill Out)
1
Biomass Pyramid (For a 2.5 year lifespan)
Biomass Pyramid
(Fill Out)
A biomass pyramid is an ecological pyramid that indicates
the total mass of organisms in each trophic level
500g.
1. The total biomass of the 3o consumer is 500 g and is
labeled for you. Label the biomass of the 2o
consumers. (Reminder: You have calculated the
average biomass eaten over a 2.5 year lifespan for
your class in column H, total)
Total Biomass of 2o consumers =
2. Determine the new ratio, R, of the total biomass of the
2˚ consumers to the total biomass of the 3˚ consumers.
R = biomass of 2˚ consumers = _________________ =
biomass of 3˚ consumers
3. Use your ratio, R, to calculate the total biomass of the 1˚ consumers by multiplying the total biomass
of the 2˚ consumers by R. Label your pyramid with the total biomass of the 1˚ consumers.
Biomass of 1˚ consumers = (R) x (Biomass of 2˚ Consumers)
Biomass of 1˚ consumers = (_____) x (_____) =
4. Calculate the total biomass of the producers by multiplying the total biomass of the 1˚ consumers by
R. Do you see a pattern in your calculations? Finish your pyramid by labeling it with total biomass
of the producers.
Biomass of Producers = (R) x (Biomass of 1˚ Consumers)
Biomass of Producers = (_____) x (_____) =
Energy Pyramid
An energy pyramid is an ecological pyramid that indicates the amount of energy in each trophic level. Only
about 10% of the energy available within one trophic level is transferred
to organisms at the next trophic level. The other 90% of that energy
Energy Pyramid
gets used by the organism or is lost as heat
(Fill Out)
1. Assume that the producers in this pyramid, plants, contain a
total of 900,000 Calories of food energy. The base is
labeled with this value.
2. Calculate the amount of energy for the 1˚ consumers by
multiplying the food energy of the producers by 0.10.
Write this value in your pyramid.
Ex. 900,000 Cal x .10 = 90,000 Cal
3. Complete your energy pyramid by calculating and labeling
the energies for the top two trophic levels.
90,000 Cal
900,000 Cal