Objective

Students will observe and understand the relationship between the kinds of birds located within the exploration area  and the types of natural bird foods found there.  They will also note how energy is passed through food chains.

Materials

• Peterson Field Guide to Eastern Birds
• Binoculars
• Variety of resources and reference material about birds

Procedure

1. Divide your students into two groups.  Take the class out on a hike around your square kilometer.  One group should be responsible for finding and identifying as many birds as they can.  The other group should look for (and identify if possible) examples of natural foods that birds might want to eat and note locations in the square kilometer where these foods are abundant.  You may wish to have the groups split up if you have enough adult supervision.
2. Back in class, have students choose a bird to study from the list of birds identified on the walk.  (If very few birds were identified, allow students to choose birds that you know are present in your square kilometer.)  Using field guides and other bird resources, have students list the natural foods their bird eats.
3. Compare the list of natural foods students’ birds eat with the list of natural foods available to these birds in your square kilometer.  How do they compare?  Does there seem to be enough natural food in your square kilometer to support the birds found there?  Why or why not?
4. Discuss the concept of food chains (see background information).  Have students construct food chains for their birds.
5. Expand the food chains into a food web and draw this to include other plants and animals that share the same square kilometer habitat and food supply.
6. Have students describe their bird’s habitat, specifically noting how their bird’s requirements for survival are met within your square kilometer.
7. Using the diagram provided in the background information, explain the carbon and oxygen cycle and its part in the food-making process.  Discuss the role of decomposers in this process.  Have students add decomposers to their food webs to complete the natural cycle of nutrients and the flow of energy.  What would happen if plants and animals did not decompose after they died?
8. Again, using the diagram provided in the background information, discuss energy pyramids and their use in representing the flow of energy within food webs.  Have students create energy pyramids using the plants and animals in their food webs.  Be sure to include the percentages of food energy transferred and lost at each step.  How does the energy of food pass from producer to consumer?
9. What do plants do with the food they make?  Are there any other organisms that use the food produced by plants?  How do animals and plants use the oxygen that plants release into the atmosphere?

Background Information

A food chain is a diagram that shows how energy moves from one living organism to another.  A food chain does not exist alone, but is a small part of a more complex system called a food web.  A food web is made when several food chains are linked.
All food chains and webs begin with an original source of energy, the sun.  Green plants use solar energy to convert water and carbon dioxide into their food through the process of photosynthesis.  Plants release oxygen into the atmosphere as a byproduct of photosynthesis.  Because plants make their own food, they are called producers.

No animal can make its food.  All animals consume plants or other animals to get energy.  An animal that eats plants is called a primary consumer or herbivore.  An animal that eats a primary consumer is called a secondary consumer or carnivore.  A carnivore that eats other carnivores is called a tertiary consumer.  Some animals eat both plants and animals and are called omnivores.  Animals not only rely on plants for food energy, but they also use the oxygen released by plants to help process their food and release energy.  Plants rely on animals as well.  When animals breathe, they release carbon dioxide, which plants use for photosynthesis.

An important part in the food chain is decomposers.  Decomposers are microorganisms in the soil that are able to break down large molecules into smaller parts.  Decomposers return the nutrients of an organism to the soil.  These nutrients are then taken up by plants as they grow and passed along through the food web as animals eat the plants, and so on.
Some energy is lost between each link in the food chain.  Because of the energy loss, each higher level has fewer living things than the level below it.

A pyramid of energy illustrates the energy transfer between the levels.  Animals at the top of the pyramid are fewer and need to eat many smaller animals to get enough energy to survive.  The primary consumers that feed on green plants are more numerous.  In a balanced ecosystem, the producers and consumers at each level have numbers that are large enough to insure their survival without depleting their food supply, thus the pyramid effect.

A pyramid shows that very little of the total energy available (10%) is transferred to the next level in the food chain.  At each stage, 90% of the energy is released to the environment as heat.  Organisms use most of their energy (releasing it to the environment as heat) to breathe, move, and function throughout the day.