Problem: What information about an owl’s diet and role in the environment can be learned from an owl pellet?

Background:

***Owl Pellets can be purchased through science supply companies.  Check the Internet

The owl pellets that will be distributed to the students come from barn owls. Barn owls are medium sized owls with large heads and long legs. The size of the cranium is due to the enhanced sight sensitivity for seeing in the dark as well as the vast aural capacity enabling the owls to hear the faintest sound made by their prey. The barn owls are found all across the globe. They are mostly found in fields and pastures because of the increased rodent population, their favorite prey. All owls have an interesting way of dealing with their food. After digesting the nutritious parts of the small animals they eat, they regurgitate all of the undigested parts in a small pellet. The pellet is composed of bones, fur and teeth. Because barn owls don't tear their prey to pieces, there is always a complete skeleton of at least one rodent in every pellet. Every bone from the skull to the last tip of the tailbone can be found. A good observer with a little patience will be able to piece together the incredible skeletal masterpiece.

An owl pellet is a roundish mass that is covered with fur and sometimes feathers from its prey. Fresh specimens are shiny and coated with mucus. Bones and other hard remains are located within the interior of the pellet. The pellet can provide evidence of the owl’s dietary habits and role in its environment.

The owl plays a role in limiting the population size of its prey. Of the animal species common to an owl’s diet, the prey species that is most abundant in the area will be the species most likely to be captured and consumed by the owl. This limits the population size of the herbivore, which in turn protects the supply of plants upon which the prey feeds. Farmers especially appreciate barn owls, which keep population of crop-eating rodents under control.

Goals: In this investigation, you will observe the external features of an owl pellet. You will then reconstruct and identify the skeletons of the prey contained in the pellet, and count the total number of organisms found. Finally, you will infer the owl’s role in its environment and its place in the food web.

Concepts: A dichotomous key is one tool scientists use to identify organisms. Each step of the key has two descriptions, and the organism being identified fits one of the two descriptions. Next to each description, the key either gives the name of the organism or directs the person to another step. The key is followed until the animal is identified.

Prediction: Using the above information, make a prediction about the outcome of this experiment and write it in your comp. book. This is also known as a hypothesis.

Examine the outside of the owl pellet. Measure and record its length and width in centimeters. Describe the external features in your lab book

To investigate the interior of the pellet, you must soften it by soaking it in water. Fill the jar halfway with water. Add a drop of dishwashing liquid and the pellet to the jar. Close the jar and shake gently for about 30 seconds. Let the jar stand for ~5 minutes and shake again. When the pellet has fallen apart, pour the contents out into the dissecting pan. Try to leave as much water as possible in the jar.

Place the contents of the pellet on a piece of paper. Pick bones, teeth, insect parts, and any other prey evidence out of the fur. Use probes, toothpicks, or forceps and tweezers as necessary. Be extremely careful not to crush any of the small bones.

Label the skulls by number, and identify them. Use the key to help in the identification process.

Try to match other bones to the skull. Using the diagrams of animal skeletons, identify each bone and record its name under its matching skull.

Use the dichotomous key to identify each set of bones you have and record all information in your lab book.

A. Create and fill in a chart on your paper – Please note that a vole is ‘equivalent’ to a mouse

B.. Use the following facts about the prey to draw a food web that is representative of your pellet

Questions to answer concerning your pellet:

How many different species remains were found in the owl pellet?

What is the likely habitat for the owl?

What is the likely diet for the owl?

Were the animals of different species? If so, how many species were represented in the pellets?

Did you find any evidence of organisms other than small mammals in the owl pellet?

What types of bones are most prevalent in the pellet? What bones are least likely to be found in an owl pellet?

What are the habitats of a barn owl’s prey? Are they similar to the habitat of the owl?

Other birds also form pellets. What would you expect to find in the pellet of a seagull?

Conclusion:

In writing up your lab report describe the role of the owl in its environment and its place in the food web. Is it an herbivore or a carnivore? Is it a producer or a primary consumer or secondary consumer? Use the information above to construct a hypothesized food web for your owl pellet.

Model:

Reconstruct and mount the skeletons. If there is time: place the bones in a beaker filled with peroxide water. Leave the bones in this solution for 24 hours. Rinse the bones with fresh water and allow them to dry. Reassemble the bones (use white glue to affix them to a piece of poster board or other cardboard).