Owl Pellet Lab
Background
Owl pellets are masses of bone, teeth, hair, feathers and exoskeletons of various animals preyed upon by raptors, or
birds of prey. These birds eat snakes, frogs, insects, mammals, and other birds. 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. 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 from common barn owls. 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.
Warning: Pellets are sterilized prior to shipment, but they have been known to still harbor salmonella (and other) bacteria.
Sterilize area and wash hands after lab.
Procedure
1. Unwrap the owl pellet.
2. Make qualitative observations about your owl pellet (sight, touch, smell).
3. Measure the approximate length and width of your owl pellet in cm. Weigh your owl pellet in grams.
Length:
width:
mass:
4. Carefully twist and break the pellet into small pieces, being careful not to break or lose any small bones.
5. Continue to break the pellet into smaller pieces and use a probe, tweezers and a toothpick to locate the bones.
You can locate any additional smaller bones by rubbing the smaller pieces of pellet between your fingers.
6. Separate and arrange similar bones. Complete the bones found table, using the bone charts and posters for
reference.
Bones found table
Bone
Prey type
Number found
Skull
Jaw
Scapula
Forelimb
Hindlimb
Pelvic Bone
Rib
Vertebrae
7. Answer the analysis questions.
8. You will be reconstructing the skeleton of a prey animal so make sure you save the bones.
9. Clean up and properly dispose of materials.
Analysis questions
1. You can determine the number of prey items found in your pellet by counting the number of skulls.
How many prey items were found in your pellet?
2. Identify the type(s) and number of prey items found.
Prey: __________ # found _____
Prey: _________ # found _____
Prey: _________ # found _____
3. Reconstruct and glue together the skeleton of an animal from the bones you removed. Use the charts and
posters for reference. If you do not have a complete skeleton you will have to draw in the missing bones (You
only need one completed skeleton for your group).
4. What do we know about the digestive system of an owl based on the pellets?
5. Owl pellets not only give us information about the diet of an owl, they also provide a habitat for other animals.
What other kinds of animals can be found in the owl pellet ecosystem?
6. Other types of birds form pellets. What would you expect to find in a seagull pellet?
7. Hawks and eagles differ from owls in that they eat their prey animals by tearing them into small pieces, picking
out the flesh and avoiding most of the fur and bones. They also have strong stomachs which can digest most of
the bone material they might eat. How would dissecting an eagle pellet compare to an owl pellet?
8. Based on the number of prey items found in your pellet (see #1), if an individual owl produces one pellet per day,
how many prey animals would a barn owl consume in a month having 30 days? Show your work.
9. Using your answer from above, how many prey animals would a barn owl consume in one year? Show your
work.
10. If owls consume ~30 percent of the rodent population in a community, what would be the population of rodents
needs to support one adult owl for a year? Show your work.