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 includemasses 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.Predictthe 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? / go to 2.
b) / At least 9 teeth on each side of its upper jaw? / go to 3.
2. a) / 2 biting teeth on its upper jaw? / go to 4.
b) / 4 biting teeth on its upper jaw? / the skull is from a rabbit.
3. a) / A skull length of 23 mm or less and brown teeth? / the skull is from a shrew.
b) / A skull length of more than 23 mm and 44 teeth? / the skull is from a mole.
4. a) / The roof of its mouth extending past the last molar? / go to 5.
b) / The roof of its mouth not extending past the last molar? / go to 6.
5. a) / A skull length of 22 mm or less? / the skull is from a mouse.
b) / A skull length of more than 22 mm? / the skull is from a rat.
6. a) / Flat molars (back teeth)? / the skull is from a meadow vole.
b) / Rounded molars (back teeth)? / 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 onpage 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