Owl Pellets
When you first see an owl pellet, you will think that it is its feces (solid waste, doo-doo or
whatever you call it), but this pellet has been ejected from the mouth. Owls are predators
and basically eat their prey whole. They eat rodents (rats, mice) and sometimes birds. In
the owl's stomach, the flesh is digested, but the fur and bones are passed back out through
the mouth.
Owl pellets can include 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 of
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.
Pre-lab Questions
Before we dissect the owl pellets and discover the rodents found within let’s review
the human skeleton. You may use your lab book or the internet.
1. Predict the similarities and differences between human bones and rodent bones
Similarities
Differences
Label the following:
Incisor
Molar
How many molars on this rodent skull? ___________
Label the following:
Upper jaw
Lower jaw
Roof of mouth
Begin the dissection here.
1. Place your pellet on a white paper towel and carefully pull the pellet apart with your
hands
2. Separate the bones from the fur. Because some of the bones are so tiny and fragile, if
you are not careful, you could either lose or crush a bone
3. Use the diagram of the rodent to identify the bones
4. Glue bones to the rodent stick sheet
List the Bones Found
Bone
Number
Skull
Jaw
Scapula
Forelimb
Hind limb
Pelvic Bone
Rib
Vertebrae
Simplified Dichotomous Key to critters found in Owl Pellets
If your critter has...
Then...
1. a) 3 or fewer teeth on each side of its upper jaw?
b) At least 9 teeth on each side of its upper jaw?
go to 2.
go to 3.
2. a) 2 biting teeth on its upper jaw?
b) 4 biting teeth on its upper jaw?
go to 4.
the skull is from a rabbit.
3. a) A skull length of 23 mm or less and brown teeth?
b) A skull length of more than 23 mm and 44 teeth?
the skull is from a shrew.
the skull is from a mole.
4. a) The roof of its mouth extending past the last molar?
b) The roof of its mouth not extending past the last molar?
go to 5.
go to 6.
5. a) A skull length of 22 mm or less?
b) A skull length of more than 22 mm?
the skull is from a mouse.
the skull is from a rat.
6. a) Flat molars (back teeth)?
b) Rounded molars (back teeth)?
the skull is from a meadow vole.
the skull is from a deer mouse.
What type of critter was in your owl pellet? ____________________________
Everything above this point must be completed in lab today
Post dissection questions:
1. Using figure 12.2 on page 153 in your lab manual describe how the forelimb of your
rodent compares to the ancestral forelimb?
2. What might have caused these evolutionary changes and or similarities?
3. What exactly are owl pellets?
4. In the owl pellet what happens to the soft parts of the prey?
5. What is the purpose of the gizzard in the owl pellet formation?
6. Where does the pellet remain until it is expelled?
7. List 5 birds that are known to regurgitate pellets.
8. How many pellets does the common barn owl produce per day?
9. What color are the pellets when fresh?
10. Why are pellets fumigated?
11. Owl pellets not only can give us information about the diet of the owl, owl pellets
also provide a habitat for other animals, in fact an owl pellet is a little ecosystem all on its
own. What kind of animals are found in the owl pellet ecosystem?
13. Would you expect to find a pellet with no bones on occasion? Why or why not?
14. Would you consider owls to be an important member of the ecosystem? Why or why
not?
15. Could an owl pellet ever be something that was used to study fossil records? Why or
why not?
Food Web