To introduce students to the idea that energy is passed from one organism to the next in a food chain.
Many middle school students have difficulty understanding the concept that energy flows from one organism to another. Students understand that animals eat each other or plants. They also understand that animals need non-living things like water, space, and shelter to survive. More challenging is the idea that when an organism dies, this energy is transferred back to the ecosystem to be reused or that some of it is lost in the process.
Most students have studied plants and have been introduced to the idea that plants make their own food. They have been told that all energy initially comes from the sun. Some students may be capable of writing the formula for photosynthesis but many have no idea how this is possible, nor do they see its relevance to their daily lives.
This lesson will serve as proof that owls eat rodents and use this energy to survive. Owls excrete the parts of the rodent that they are unable to digest, leading students to infer that they are recycled in the soil. Using commercial owl pellets, students can try to identify the type of rodent eaten by the owl. Students are capable of creating a food chain based on prior knowledge: Owl-vole-grain or seeds-sun.
Students' attention should be drawn to the transfer of energy that occurs as one organism eats another. It is important that students learn the differences between how plants and animals obtain food and from it the energy they need. (Benchmarks for Science Literacy, p. 120.)
At this point, the teacher has the option of discussing one food chain or creating a food web using other animals that might live in the forest.
Begin this lesson by asking these questions:
- Have you ever been camping at night?
- What sounds did you hear?
- Were you afraid?
- What do you know about owls?
- What species of owls live in our area? What species live in North America?
These questions should lead to a lively discussion which will allow you to assess what the students already know about owls. After going over the above questions, brainstorm a class list of possible food sources for an owl that might live in a local ecosystem.
- Can you estimate the number of small mammals an owl might eat in one day? How about one week?
- Is an owl harmful or helpful to man? How?
Researching an owl
Before students work with the owl pellets, they will conduct some research on owls to gain more knowledge about them. The following activity can be done by individuals or by students working in pairs. Provide each student (or pair of students) with a copy of the Owl Research Notes student sheet. Also, assign each student or pair a North American owl to research. The Owls of North America page on The Owl Pages website is useful to generate such a list.
Create a research timeline for the students. One or two class periods are suggested, with students completing their research at home if necessary. Students can report orally on their research or hand in the worksheet to be graded by the teacher.
Recreating the skeleton of a small mammal from an owl pellet
- Instruct students to unwrap the pellet from the aluminum foil.
- Students should carefully tease the bones from the fur using toothpicks.
- Tell students to sort the bones into sections of egg cartons for safe storage and future classification. Make sure students label the top of the egg carton with the their names and period. (Sorting may take 2-3 class periods, gluing and identification of bones 2-3 classes.)
- Students should use the vole skeleton model to arrange the bones on a large index card.
- Then, students should glue the bones in place and label them.
- Students may "trade" bones with other students to complete their skeleton.
- Any bones that may be missing can be drawn in using a fine tip black marker.
- Students should turn in the completed skeleton for evaluation.
Have students respond to the following, either in writing or in a class discussion:
- Analyze the bone structure of the skeleton, and try to identify the small mammal that was eaten by the owl to survive.
- List all food possibly eaten by that small mammal for energy.
- Where does the energy in the food come from?
- What happens to the energy when the owl dies?
Have students construct a food web for the ecosystem using words or pictures. You could also have students write a short response to the following scenario:
A farmer in New Jersey is trying to control the number of mice in his barn by using pesticide. He put four containers of pesticide in the corners of his barn. He waited one month and did not notice a huge difference in the number of mice running around in his barn. He gathered up the empty containers and disposed of them using a large black plastic bag, which he tossed in the garbage pile behind the barn. He decided to purchase two barn cats from the local pet rescue. His land borders on a local park, which is protected by law as a wildlife refuge. How might the Barn Owls in this ecosystem be effected over the next three months by the farmers attempt to solve his problem?
See Birds of Prey, a complementary Science NetLinks lesson that targets Benchmark 5D Interdependence of Life 6-8 #2, and extends the ideas in this lesson.
You can also extend the ideas in this lesson with the Science NetLinks lesson called Burrowing Owls. Though targeted to high-school students, this lesson includes suggestions that can make it appropriate for use with students at the 6-8 level.