Owl Pellet Dissection Lab

Owl Pellet Dissection Lab
Introduction
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 or in small pieces. Owls feed early in the evening and regurgitate
a single pellet approximately 20 hours after eating.
Predatory mammals such as bobcats and wolves have teeth to grind up bones
and claws, and, a digestive tract adapted to pass these ground parts. Owls, on the
other hand, do not have teeth for grinding and cannot pass whole bone and claws
through their digestive tract safely. The protein enzymes and strong acids that
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 a bolus (or wet slimy pellet). Depending upon the prey eaten, the undigested
portions may include beaks, claws, scales, or insect exoskeletons. This type of
material has little nutritional value and must be passed from the body. In this
process even the most fragile bones are usually preserved unbroken.
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Owl Pellet Dissection Lab
Scientists take advantage of this adaptation by collecting these pellets and
examining their contents. Since owls are not very selective feeders, these pellets
can be used to estimate the diversity of available prey. The contents are also a
direct indicator of what an owl has fed on; information that is crucial for species
management and protection.
The owl pellets that you will be examining in this lab have been
collected and fumigated from common barn owls (Tyto alba). Owl
pellets themselves are ecosystems, providing food and shelter for
communities that 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.
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Owl Pellet Dissection Lab
Materials:
• owl pellet (wrapped in aluminum foil)
• brown glass specimen jar (cap optional)
• dishwashing detergent or hand soap
• cheese cloth
• forceps
• 2 dissecting mounts
• dissecting probe
• dissecting pan/tray (located at station)
• several sheets of white paper (recycled)
• 2 specimen dishes and/or watch glasses/petri dishes
• metric balance
• ruler
• stereoscopic dissecting microscope
• magnifying glass
• water
• paper towel
• desiccating oven (high temp.)
• latex gloves (pair for each partner)
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Owl Pellet Dissection Lab
Procedure:
1. Unwrap and examine the outside of the owl pellet. Put all data and observations
on the Data, Observations, & Analysis page. Describe the external
features. Measure and record its length and width in centimeters. Measure
and record the owl pellet mass in grams.
2. To investigate the interior of the pellet you must soften it by soaking it
in water. Fill the specimen jar 3/4 full with tap water. Add a drop or two
of dishwashing liquid or hand soap and the pellet to the jar. Close the
jar with a cap or cover with your gloved hand and shake gently for about
30 seconds. Let the jar stand for five minutes and shake again for 30
seconds.
3. When the pellet has fallen apart, have your partner hold the cheese cloth,
and slowly pour the contents of the jar over the cheese cloth. Be careful
not to allow any animal fragments, bone, or fur wash into the sink.
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Owl Pellet Dissection Lab
4. Place the cheese cloth on a piece of white paper. Pick bones, teeth, insect
parts, and any other prey evidence out of the fur and place all prey evidence
(except skulls) in a specimen dish or watch glass. Place the skulls on a second
sheet of paper. Use probes, dissecting mounts, or forceps, as necessary, but
proceed carefully to avoid crushing any small bones. Separate the fur and
other soft matter as you search for bones by placing them in a separate
specimen dish or watch glass.
5. Label the skulls by number, and use this dichotomous key to
identify them. Record the species of each skull on your answer sheet.
6. Try to match other bones to each skull. Use the preserved specimens
and the diagrams of animal bone structures provided to identify each
bone and record its name under its matching skull on your answer
sheet.
7. Use the links provided with the dichotomous key to find the likely habitat and
diet of each species found in the pellet. Record the information on your answer
sheet.
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Owl Pellet Dissection Lab
8. Talk with other groups and find the types and number of species found in all of
the pellets. Record this in Table 2.
9. Once all bones have been identified, collect your bones in the specimen dish.
Carefully dry as many as you can with one or two pieces of paper towel. Add
the other organic matter (i.e. fur and small miscellaneous pieces). Then, make
a small mark on your specimen dish to be able to identify it, and place your
entire specimen dish in a high temperature oven for drying. Check the organic
matter after 24 hours to record the biomass.
10. Complete the Answer Sheet and make sure both team members
have a copy.
11. Complete the Homework for this lab.
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Owl Pellet Dissection Lab
References
“Alcorn/AP Environmental Science Owl Pellet Dissection.” Dr. Decino’s webpage.
Carlsbad High School. 27 Oct. 2008 .
Gautschi, D. Tobias. “Owl Pellet Lab.” Mr. Gautschi’s Home Page. El Dorado High
School. 27 Oct. 2008. .
Radcliffe, G. “HUMAN BODY Lab 3: Owl Pellet Dissection.” Human Body Unit.
Centreville Middle School. 27 Oct. 2008 .
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Owl Pellet Dissection Lab
Images
Image:Shituan.jpg (Pellets from a long eared owl)
This file is licensed under the creative commons attribution sharealike 2.5 license. in short: you are free to
share and make derivative works of the file under the conditions that you appropriately attribute it, and that
you distribute it only under a license identical to this one. official license
Barn owl images (both adult and chicks)
florinorfolk. “Magic Owls.” weblog post. photorama . 29 may 2008. flickr. 27 Oct. 2008. .
Image: close-up of mole.jpg
Permission is granted to copy, distribute and/or modify this document under the terms of the gnu free
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invariant sections, no front-cover texts, and no back-cover texts.
Image: northern spotted owl.usfws-thumb.jpg
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