5-12 Middle/High School
You can use this resource as a stand-alone activity or as an extension of an owl pellet dissection. Students use the phenomenon of owl pellets to construct a model food web for barn owls. Using the food web and simple calculations, they track the flow of energy and biomass through the food web, enforcing the concept of matter and energy conservation.
Depending on grade level, you may wish to select some or all of the analysis questions. Questions 1 and 2 address energy transfer, and questions 3 through 5 require calculation of biomass, consumption needs, and energy at each tropic level. Where appropriate, content for high school students is marked HS and content for middle school students is marked MS.
How do energy and mass flow through a food web?
MS-LS2-3. Develop a model to describe the cycling of matter and flow of energy among living and nonliving parts of an ecosystem.
HS-LS2-4. Use mathematical representation to support claims for the cycling of matter and flow of energy among organisms in an ecosystem.
Planning and Carrying Out Investigations
LS4.D Biodiversity and Humans
Patterns
Prior to taking students outside, locate an area where they can easily dig up a weed or small plant without harming school landscaped areas. Ensure that the terrestrial plants have roots, stems, and leaves after students dig them up. If the school grounds are not appropriate for plant samples, purchased plants like coleus, marigolds, and pansies work well.
To dispose of duckweed, place it in a resealable bag, freeze it for several days, and then dispose of the bag in the classroom trash. Do not dump duckweed into a body of water.
1. Using the information in the overview or the owl pellet dissection results, construct a simple food web for a barn owl. Label the trophic levels and type of consumer. Include the sun as the energy source for the plants.
See food web above.
2. Based on the data in the overview, a barn owl’s diet is about 50% voles, 40% mice, 5% rats, and 5% shrews. Assume the barn owl is regurgitating two pellets a day and each pellet has four skulls. Determine the number of each type of animal the owl consumes during a 24-hour period. Use only whole numbers. Place the numbers on the data table. *If you completed the owl pellet dissection, record the actual number and type of animal consumed. Get data from another group to represent the second pellet.
See the data table below.
3. Use the diet chart and complete the calculations for the table below.
See the data table below.
Answers will vary depending on the actual animals selected for the food web.
1. What is the total daily mass of food consumed by the owl (grand total)?
547 g
2. Calculate the percentage of mass each type of animal contributes to the owl’s total daily consumption and write it in the table above.
See table above.
3. Use the diet chart and complete the calculations for the table below.
See the data table below.
1. Use the food web to identify the pattern in food mass consumed for the primary and secondary consumer trophic level.
With each trophic level, mass consumed increases.
2. The sun provides 100% of the energy needed by plants. Only 10% of energy is transferred from a lower to higher trophic level. What percentage of the initial energy does the owl receive? Show the calculations.
Answers will vary depending on the food web, but the sun is 100% energy, producer level is 10%, primary consumer is 1%, secondary consumer is 0.1%, tertiary consumer is 0.01%, and so on.
3. Using the laws of conservation of matter and conservation of energy, how can the pattern be explained?
As an organism obtains food, the mass and energy of the food are used to produce cell growth and maintain cell functions. Waste mass is produced and eliminated by organisms and waste heat energy is often produced and released into the environment. Only 10% of energy consumed at a trophic level is available for consumption at the next higher level.
4. If an owl were in a setting where it could consume only rats, how would that change the food web, the number of trophic levels on the web, and the percentage of initial energy that is transferred to the owl?
(HS) Rats weigh almost 10 times more than the average mouse or vole. Consequently, owls would need to eat fewer rats than they do voles and mice. A possible scenario could be 2 rats daily compared to 8 or 9 mice and voles. Since rats are omnivores, that means the rats would be eating on a higher trophic level. The higher trophic level decreases the available amount of energy again by 90%. If rats are eating herbivores, they receive a total of 0.1% of the initial energy input. If they eat rats, only 0.01% of energy is available.
Owl pellet dissection gives students a unique view of an owl’s natural habitat.
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*Next Generation Science Standards® is a registered trademark of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.
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