J5OwlPel
OWL PELLETS
INTRODUCTION
Owl pellets are the undigested remains of prey ingested by an owl. The owl swallows its prey
whole, and during the process of digestion, the soft parts of the prey are dissolved and passed on
to the intestine for absorption. The hard, non-digestible parts-bones, teeth, fur, feathers, and
chitonous remains of insects are compressed in the gizzard and passed on to the proventriculus,
the first chamber of the owl’s stomach, where the pellet remains until it is expelled. These pellets
are not eliminated as feces, but are regurgitated through the mouth.
Pellets are not found exclusively within the owl families. There are many species of birds known
to regurgitate pellets: hawks, eagles, kites, harriers, falcons, and even robins are some of the more
familiar ones. Out of all types of pellet ejectors, the efficiency of the process is probably as high
in owls as in any other bird.
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 fumigated to eliminate the presence of any insects and then individually
wrapped for preservation. Unless otherwise stated, the pellets in this lab are from the family
Tytonidae and more specifically, the Common Barn Owl (Tyto alba).
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
glue
hand lens
paper plate
rulers
balance
bone sorting charts
PROCEDURE
Part 1: Pellet dissection
1. Work in pairs or as directed by the teacher.
2. Remove the pellet from the aluminum foil.
3. Mass the pellet and record the mass in Table 1.
4. Measure the length and width of the pellet and record these measurements in Table 1.
5. Place the pellet in a paper plate. Carefully separate the bones from dried fur or feathers using
a teasing needle and forceps. Place the bones in another part of your plate.
6. Carefully clean the bones and sort them according to type, skulls, jaws, vertebrae, etc.
7. When you are sure that all bones have been removed from the fur, you may discard the fur
and/or feathers.
8. Identify the animals found in your pellet comparing your skulls to the skulls in the picture
keys.
9. Using a dot of glue, attach each bone beside the matching bone on the diagram on your lab
sheet. You will sometimes have many of each type of bone and they will all be glued beside
the diagram.
10. Record the types and numbers of animals in Table 2 and in the chart on the board.
11. When the last group has recorded their data on the board, copy the class data in Table 2.
Revised 8/09
ASIM Biology: Environment
Page 1 of 12
Owl Pellets - J5OwlPel
Part 2: 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: a
number pyramid, a biomass pyramid and an energy pyramid.
Each pyramid you construct will consist of four trophic levels.
The top of each will relate to your owl, the only tertiary consumer
(3o). The next level down will relate to the owl’s prey, the
secondary consumers (2o). 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 consumers, (1o).
The base of each pyramid will relate to the organisms eaten by the
primary consumers, the producers.
Use the information obtained from your owl pellet dissection to
construct the ecological pyramids below.
Number Pyramid, for one 24 hour period
A number pyramid is an ecological pyramid that indicates the total number of
organisms in each trophic level
1. Draw your pyramid, labeling the number of 3o, 2o and 1o consumers.
(Reminder: There is only 1 owl, which is the 3o consumer, and you have
calculated the average number of prey found in each pellet for your
class.)
2. Determine the ratio, R, of the number of 2o consumers to the number of 3o consumers.
R = # 2˚ consumers
# 3˚ consumers
3. Use your ratio, R, to calculate the number of 1o consumers by multiplying the number of
2o consumers by R. Label your pyramid with the number of 1o consumers.
# 1o consumers = R (# 2˚ consumers)
4. Calculate the number producers by multiplying the number of 1o consumers by the ratio,
R. Finish your pyramid by labeling it with the number of producers.
# producers = R ((# 1˚ consumers)
Biomass Pyramid, for a 2.5 year lifespan
A biomass pyramid is an ecological pyramid that indicates the total mass of
organisms in each trophic level
1. Draw your pyramid and label the total biomass of the 3o consumer,
assuming the owl’s biomass is 500 g. Label the biomass of the 2o
consumers. (Reminder: You have already calculated the average
biomass eaten over a 2.5 year lifespan for your class)
Revised 8/09
ASIM Biology: Environment
Page 2 of 12
Owl Pellets - J5OwlPel
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 (biomass of 2˚ consumers)
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.
Energy Pyramid
An energy pyramid is an ecological pyramid that indicates the amount of energy in each trophic
level. According to the terms of thermodynamics, only about 10% of the energy
available within one trophic level is transferred to organisms at the next trophic
level.
1. Assume that the producers in this pyramid, plants, contain a total of
500,000 Calories of food energy. Label the base of your pyramid 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.
3. Complete your energy pyramid by calculating and labeling the energies for the
top two trophic levels.
Revised 8/09
ASIM Biology: Environment
Page 3 of 12
Owl Pellets - J5OwlPel
Revised 8/09
ASIM Biology: Environment
Page 4 of 12
Owl Pellets - J5OwlPel
Revised 8/09
ASIM Biology: Environment
Page 5 of 12
Owl Pellets - J5OwlPel
Revised 8/09
ASIM Biology: Environment
Page 6 of 12
Owl Pellets - J5OwlPel
Identifying Owl Pellet Contents*
How to
measure
the jaw
Tooth
types
Jaw Length
Revised 8/09
ASIM Biology: Environment
Lobed
Angled
Pointed
Page 7 of 12
Owl Pellets - J5OwlPel
Rat
Vole
Mouse
Shrew
Bird
Jaw Length (mm)
17-30
15-20
10-15
7-14
15-40
Tooth Type
Lobed
Angled
Lobed
Pointed
None
Skull and Jaw
Shoulder Blade
Hip
Upper Leg
Lower Leg
Rib
Back Bones
Foot
Revised 8/09
ASIM Biology: Environment
Page 8 of 12
Owl Pellets - J5OwlPel
STUDENT DATA SHEET
OWL PELLETS
Name:_______________________
Date: _______________________
DATA
Part 1
Table 1.
Owl Pellet Measurements
Mass
Length
Width
Table 2.
Kinds and Numbers of Animals Found in Owl Pellets
Vole
Shrew
Bird
Your Data
Class Data
Mole
Rat
ANALYSIS
1. Construct a bar graph from the classroom data collected above.
2. Assuming that the barn owl regurgitates one pellet per day, how many prey items would the
owl that produced your pellet consume per year?
3. During the nesting season the young need an enormous amount of food for growth. If the nest
contains three young and each of the young eat five mice per night for a month and the two
adults eat four per night, how many mice would the parents have to capture in 30 days?
Revised 8/09
ASIM Biology: Environment
Page 9 of 12
Owl Pellets - J5OwlPel
4. Environmentalists are concerned about the accumulation of certain poisons in predators. Why
do you suppose owls, eagles, swordfish, humans and lions are often the most threatened
organisms of a community that are exposed to DDT or mercury?
5. Placing the owl at the highest trophic level, create a food web using the following items: vole,
deer mouse, mole, house mouse, weasel, shrew, snake, starling, frog, salamander, spider,
grubs, earthworms, centipedes, crane fly, seeds, plants, roots.
6a. What valuable information do you think can be gained by studying the owl pellet?
b. List other information that can be gained by studying owl pellets.
7. What are owl pellets?
8. What happens to the soft parts of the prey?
9. What is the purpose of the gizzard in the owl pellet formation?
10. Where does the pellet remain until it is expelled?
11 These pellets are not eliminated as _________________, but are regurgitated through
the ___________________.
Revised 8/09
ASIM Biology: Environment
Page 10 of 12
Owl Pellets - J5OwlPel
12. List 6 other birds that are known to regurgitate pellets.
13. Of all the birds that are pellet ejectors, which type of bird is probably the most efficient at this
process? ________________________________
14. How many pellets does the common barn owl produce per day? ________________________
15. What color are the pellets when fresh? ____________________________________________
16. Describe the appearance of a dry owl pellet.
17. The pellets are from what owl family? _____________________________________________
18. Why are the pellets fumigated?
19. How do food webs and food chains differ?
20. Why does the number of organisms decrease as you move up the pyramid level?
21. In terms of energy flow in an ecosystem, why is the amount of energy passed from one trophic
level to the next so small? Since we know energy cannot be destroyed, account for the loss of
energy that occurs between the prey and the owl.
22. We know that about 50% of the energy in an organism is not digested by the consumer and is
simply passed through as waste or feces. Is the energy stored in the feces lost to the
ecosystem? Why or why not?
Revised 8/09
ASIM Biology: Environment
Page 11 of 12
J5OwlPel
Part 2
Table 3
B
C
D
E=
D/# of grps
Biomass
Number
found in
pellet
Total
number
found by
class
Average
number
found per
pellet for
class
A
PREY
TYPES
House
Mouse
20 g
Vole
40 g
Shrew
5g
Brown Rat
240 g
Bird
80 g
F=
E x 365
Average
number
eaten per
year (1
pellet per
day:365
days)
G=
BxE
H=
G x 365
I=
H x 2.5
Average
biomass
eaten per 24
hours (g)
Average
biomass
eaten per
year (365
days) (g)
Average
biomass
eaten over
a 2.5 year
lifespan (g)
Other
Total
Drawings of pyramid of number
Revised 8/09
Drawing of biomass pyramid
ASIM Biology: Environment
Drawing of energy pyramid
Page 12 of 12