The Owl Pellet Dissection Lab
or “The Murder of Mickey Mouse”
Introduction:
Owls are carnivorous birds who usually eat their prey whole. Owls usually eat small rodents such as meadow voles, shrews and moles, but larger owls can kill birds or even rabbits. Although owls swallow their prey whole, they cannot digest all the parts of their prey. The indigestible parts are compressed into pellets and regurgitated.
Since the prey was eaten whole, pellets can contain entire skeletons, fur, whiskers and even tails! When looking at a pellet, ecologists often use a series of directions called a dichotomous key to determine what animals were eaten. In this lab, you will use a simplified dichotomous key, in which the skull and teeth are the major bones used to identify the prey.
Owls usually regurgitate two pellets a day: one at the day roost (the place the owl perches during the day) and one at the hunting grounds. It takes between six and seven hours for a pellet to come up.
Procedure:
1.Form a group of two or three people.
2.Each person in your group should write their name on their own copy of the sheets titled “Owl Pellet Dissection Worksheet” and “Student Bone Pile”. Each person in the group will hand in their own copy of these sheets (that is, one copy per person will be handed in, NOT one copy per group).
3.Measure the length and width of the pellet and write them on the Owl Pellet Dissection Worksheet.
4.Carefully unwrap your pellet on a piece of paper towel.
5.Gently pull apart the owl pellet and separate the pieces into 2 or 3 equal piles (depending on whether there are 2 or 3 people in your group). You may use your fingers or forceps (dissection tweezers) to pull apart the pellet.
6.Each person in your group should take one pile of owl pellet pieces to work on.
7.Using your fingers or forceps, carefully separate the bones from the fur or feathers. Take special care removing skulls and jaws because they are the best way to identify animals.
8.Compare the bones you find to the diagram of the rodent skeleton. Place each bone in the appropriate box of the sheet titled “Student Bone Pile”.
9.When you have found all of the bones that you can, count them and fill out the chart on the Owl Pellet Dissection Worksheet. Write your own totals, then your group’s.
10.Try to put together the skeleton of an entire rodent on the Owl Pellet Dissection Worksheet of one person in your group. You will probably have to use bones from all of your piles to do this. (If you cannot make a complete skeleton, make it as complete as you can.)
11.Have Mr. Primmer photograph your assembled skeleton.
12. Answer the questions on the back of this page.
13.When you are finished, tape down all the bones of the complete skeleton and the leftover bones on your individual Student Bones Pile sheets.
Your name: ______
Group members: ______
Owl Pellet Dissection Lab – Questions
Answer the following questions in complete sentences.
1.How many animals did this owl eat? (Hint: if you got two sets of forelegs, the owl must have eaten at least two animals…etc.)
______
2.Compare the skulls you found to the dichotomous key. What kind of animal(s) has the owl eaten? (Hint: the teeth are most easily counted by using forceps to pull them out of the skull!) Provide common name and scientific name.
______
3.What do the contents of this pellet tell you about the owl’s diet?
______
4.What habitat do you think this owl would hunt in? Why?
______
5.Draw a complete food chain or food web that includes the owl and the animals you found in the pellet.
6.What trophic level is the owl?
______
Your name: ______
Group members: ______
Student Bone Pile
HumerusFemurLower Jaw
Tibia/FibulaVertebrateShoulder Blade
Ulna/Radius Ribs Pelvic Bones
Skulls
Your name: ______
Group members: ______
Owl Pellet Dissection Worksheet
Owl Pellet Length: ______
Owl Pellet Width: ______
How many of following bones did you find?
Student Total / Group TotalHumerus
Femur
Lower Jaw
Skull
Vertebrate
Shoulder Blade
Ulna/Radius
Ribs
Pelvic Bones
Tibia/Fibula
Attempt to re-assemble a complete mouse below: