FF-01: Owl Pellets
An activity from the
Environmental Volunteers
Program Area:
Foothills Ecology
Grade Levels: 3-6
EV Learning Objectives:
1. Owls are nocturnal
carnivores that eat a variety
of rodents and sometimes,
birds.
2. Owls have specific
adaptations that make them
successful hunters.
3. Owls eat their prey whole
and regurgitate the parts that
they cannot digest.
4. Owls are consumers in a
food chain.
EV Sustainability
Principals:
E. Understanding the beauty
of our planet, the elegance of
natural systems, and the
interconnectedness of all its
parts.
Overview: Students will identify and compare bones found in
dissected owl pellets to understand an owl’s relationship within its
food web.
MATERIALS LIST
Visual
Owl Pellets
Plates
Spoons
Skewers
Spray Bottle with water
Small Ziploc bags
Permanent marker
Owl study skin
Rodent study skin
Wet Wipes
CALIFORNIA EDUCATIONAL STANDARDS
All standards are for science unless otherwise noted. 1
Third Grade
• 3.a Students know plants and animals have structures that
serve different functions in growth, survival, and
reproduction
EEI Learning Objectives
• 3.a-1 Identify that plants and animals have different
structures that allow them to grow, survive, and reproduce
by using/consuming the goods and ecosystem services
provided by the natural systems.
Fourth Grade
• 2.b Students know producers and consumers (herbivores,
carnivores, omnivores, and decomposers) are related in
food chains and food webs and may compete with each
other for resources in an ecosystem.
Fifth Grade
• 2.a Students know many multicellular organisms have
1
Note about EEI Learning Objectives: this learning station supports these objectives of the Education
and the Environment Initiative’s Environmental Principles and Concepts. As the learning objectives do
not have their own numbering convention, the one used here show the number of the standard before the
dash and the number after the dash is the bullet point from the list of objectives for that standard.
FF-01: Owl Pellets
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specialized structures to support the transport of materials
EEI Learning Objectives
• 2.a-1 Describe how respiration, digestion, waste disposal, and transport of materials
result in byproducts.
Sixth Grade
• 5.b Students know matter is transferred over time from one organism to others in the food
web and between organisms and the physical environment.
EEI Learning Objectives
• 5.b-5 Recognize that the transfer of matter through an ecosystem generates byproducts
(e.g., matter and heat energy are dissipated during transfers between levels in the food
web).
ACTIVITY
BEFORE CLASS SETUP
You may want to open up the pellets and spray them with water to soften them. This will make
them easier to work with, but it will also make them smell!
INTRODUCTION
(Time required: 1-2 minutes)
Note: The majority of this kit should be actual dissection of the pellets and the discussion of
what is found. Keep your introduction as short as possible.
Show the students the owl mount (or study skin). Explain to them the correct way to touch the
owl (two fingers and always in the direction of the feathers) and let them touch the owl.
Explain: Owls are hunters and today we are going to look at some of the adaptations they have to
help them hunt.
Explain: First I want you to think about your eyes. When you go from a brightly lit area to a
dark area, your eyes need time to adjust. But an owl’s vision adjusts more quickly which makes
it easier for an owl to see in the dark.
Ask: How would this help an owl hunt?
An owl would be able to see its prey, even when it is dark out. This is especially
important because owls are nocturnal.
Explain: Another thing that owls can do is turn their heads 180 degrees so they can see what is
behind them.
Ask: How would this help an owl to hunt?
An owl would be able to see a bigger area which would make it more likely to find its
prey.
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Ask: Now let’s look at the feathers. How is the edge of the owl wing different from the wings of
other birds?
The feathers have a soft fringe instead of being stiff.
Explain: These soft feathers allow an owl to fly silently.
Ask: How would flying silently allow an owl to be a better hunter?
Prey wouldn’t be able to hear the owl coming. More importantly, the owl is able to hear
his prey.
Ask: Look closely at the owl’s feet. What do you notice?
The owl has sharp claws.
Ask: Now what do you notice when you look at the beak?
It is sharp and curved like a hook.
Ask: Why would an owl need sharp claws and a sharp, hooked beak to hunt?
For grasping prey, tearing flesh, and pulling apart the meat of larger prey.
Explain: When an owl eats, he swallows his prey whole or in large chunks. The owl's inner
organs sift, sort and absorb the nourishment from the food. The owl has an inner "garbage
compactor" which mashes the indigestible parts into a pellet, which he spits out. (The visual is
helpful in this explanation.) If you look inside the pellet you can find bones and figure out what
the owl ate.
Ask: Who wants to look inside an owl pellet?
If any of the students seem squeamish about dissecting the pellets, just begin the activity.
That student will most likely get into the activity as other students start finding things in
their pellets. If not, the student will still be getting the information to meet the learning
objectives.
ACTIVITY 1: Pellet Dissection
(Time required:10-12 minutes)
Pass out the plates, tweezers, toothpicks, and magnifying glasses.
Pass out the pellets – two students receive one pellet to share.
Show a previously dissected pellet and the mounted bones to show students what to look for.
Have students start dissecting the pellets while you pass out bags so students can keep the bones.
As students dissect their pellets ask them about what they find. Young students can identify “leg
bones”, ribs, etc. while older students can be more specific and may be able to identify specific
animals using the bone chart provided.
ACTIVITY 2: Conclusion
(Time required:2-3 minutes)
Ask: Why do you think we didn’t find any plants in the owl pellets?
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Owls are carnivores so they don’t eat plants.
Explain: Owls still need some of the nutrients from plants even though they eat other animals.
Ask: How do owls get the nutrients from plants if they don’t eat the plants?
Owls eat small animals and those small animals eat plants. Sometimes the small animals
have plants in their stomachs that they haven’t finished digesting. Also, since the small
animals do eat the plants they have some of the same nutrients as the plants.
Ask: What do you think would happen if owls weren’t around to eat some of these small
animals?
The small animals would multiply until they didn’t have enough food to eat. If the small
animals ate all of the plants, then other herbivores wouldn’t have food either.
TWO-MINUTE WARNING
(Time required: 2 minutes)
Have students collect whatever they want to keep in their bags. Collect the plates and dissection
utensils so the table is clear for the next group.
CLEAN UP
At the end of the service, discard any leftover pellet material and return all other materials to the
kit.
ALTERNATE SCRIPTS
HELPFUL HINTS
GLOSSARY
Adaptation – a change in a structure that helps an animal survive in a given
environment
Carnivore – an animal (or plant) that eats meat
Food Chain – a chain from a food source to the final consumer
Food Web – the interconnection of many food chains
Nocturnal – active at night
Raptors – birds that are predators
Regurgitate – to rush or surge back
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SCIENCE BACKROUND
Most owls are nocturnal birds of prey. They fly silently through the sky, hunting small rodents,
insects and, occasionally, birds. Equipped with excellent hearing and highly developed binocular
vision, they are extremely efficient hunters in low or no light conditions. An owl’s eyes’ retina
lack cones hence they do not perceive color. However, the pupils can be adjusted independently,
which gives owls more flexibility in spotting their prey. Owls have ears that are set at different
levels on each side of their heads, so they can hear from different distances and heights. This
difference in ear alignment enables owls to pinpoint their prey accurately in the dark.
Some people mistakenly believe that owls turn their heads 360°. Owls are capable of
more than 180° turns, which allows a much greater field of vision.
Owl flight is silent. The feathers of most birds are stiff on the edges. Owls have a soft
fringe to cushion their wing beats. Silent flight is important both so that the prey does not hear
the owl, but also so that the owl can hear the prey.
Like all birds of prey, owls have beaks with a sharp hook for tearing flesh and sharp
claws to help the owl grasp his prey and pull apart the meat. When an owl eats, he swallows his
prey whole. His internal organs then sift through the material and digest the meat of the prey.
Since bones, scales, teeth, fur and feathers cannot be digested, the gizzard compacts them into
pellets which the owl regurgitates 18-20 hours after having eaten.
Owls have a poor sense of smell. In fact, owls are one of the few predators known to eat
skunks.
Owl pellets are masses of bones, teeth, hair, feathers, scales and insect skeletons. They
are produced and regurgitated, not only by owls, but also by hawks, eagles, and other raptors
(birds of prey) that swallow their prey whole or in large pieces. Proteolytic enzymes (protein
digesters) and strong acids that occur in high concentrations in the stomachs of raptors dissolve
the soft parts of the prey. The relatively weak stomach muscles of the bird form the undigested
fur, bones, feathers, etc. into wet, slimy pellets. In this process, even the most fragile bones are
usually preserved unbroken. Because the pyloric opening of the stomach into the intestine is
narrow, only finely divided materials pass into the intestine. As a result, only tiny bones
occasionally pass through the digestive system. Each whole owl pellet usually contains virtually
complete skeletons of the animals that the owl ate the night before the pellet was formed.
Barn owl pellets are egg-shaped masses averaging 47 mm in length by 33 mm in width.
Their dry weight is about 52 percent fur and 48 percent bone; each pellet contains an average of
3.3 animals.
From these data, it is estimated that an adult barn owl requires 80 to 100 grams of prey
daily. The kinds of prey species in each pellet varies, but a sample of 135 barn owl pellets in the
Pacific Northwest contained the following averages: 2.5 voles (Microtus), 0.7 shrews (Sorex),
and 0.1 of the other species. Major factors determining the kinds and ratios of species found in
owl pellets are where the owl lives and what prey are seasonally most abundant.
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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 (larvae). The larvae
metamorphose near the surface of a pellet in cocoons made of the fur.
EV SUGGESTS- TIPS, TRICKS, AND NEWS
http://www.owlpages.com/physiology/digestion.html The Owl Pages. An excellent source of
information on owl digestion with photographs.
REFERENCES
Duke, G.E., Jegers, A.A., Loff, G., and Evanson, O.A. (1975) Gastric digestion in some raptors.
Comp. Bioche. Physiol. 50A, 649-656.
Doerksen, George Peter. (1969) An analysis of barn owl pellets from Pitt Meadows, British
Columbia. The Murrelet. 50(1), 4-8.
Farner, D.S. (1960) Digestion and the digestive system. In Biology and Comparative Physiology
of Birds, Vol. 1. (Edited by Marshall, A.J.) Academic Press, New York.
Glading, B.D., Tillotson, D.F., and Sellect, D.M. (1943) Raptor pellets as indicators of food
habits. Calif. Fish & Game. 29,92-121.
Kostuch, T.E., and Duke, G.E. (1974) Gastric motility in great horned owls. Comp. Biochem.
Physiol. 51A. 201-205.
Reed, C.I., and Reed, B.P. (1928) The mechanism of pellet formation in the great horned owl
(Bubo virginianus). Science Wash. 68. 359-360.
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