Understanding Owl Pellets (Mark Rothenay)
Title: Understanding Owl Pellets
Principle(s) Investigated: Understanding food webs and energy transfer.
Grade 6: Ecology, life science
5b. Students know matter is transferred over time from one organism to others in the food web and between organisms and the physical environment.
5c. Students know populations of organisms can be categorized by their functions in an ecosystem.
5e. Students know the number and types of organisms an ecosystem can support depends on the resources available and on abiotic factors such as quantities of light and water, range of temperature, and soil composition.
Grade 7: Structure and Function in Living Systems
5a. Students know that plants and animals have levels of organization for structure and function, including cells, tissues, organs, organ systems and whole organisms.
Grade 9-12: Ecology, life science
6e. Students know a vital part of an ecosystem is the stability of its producers and decomposers.
Materials: Owl Pellet
Toothpick
Black paper
Gloves
Small mammal bone identification chart
Tweezers (optional)
Magnifying glass (optional)
Glue
Procedure:
1. Before lab, briefly explain what an owl pellet is and how it is formed.
2. Place students in groups of two with one owl pellet, one sheet of black construction paper, one set
of tweezers, one pair of toothpicks, and owl pellet identification worksheets.
3. Have the students dissect the owl pellet separating bones from fur. Students will also separate
bones and determine how many prey species are inside the pellet as well as determining the
type of species.
4. Students will look for any sign of insect life inside the pellets and if there is, count how many there
are and what types.
5. Have the students build a food web.
6. Have the students build the prey skeleton or I.D. the bones.
Student prior knowledge:
1. Students should have prior knowledge on tissue systems including the skeletal systems.
2. Students should have some prior knowledge on prey/predator dynamics.
Explanation:
The owl pellet dissection lab gives students a hands on approach on what is a food web. Students can also find small insect remains in the pellets showing a further step in the food chain. Too many food web charts show a trail that ends to the owl itself when a more accurate picture would show the owl pellets coming from the owl going back to the beginning of the food chain that nourishes fungus and insects that are in turn preyed upon by mammals (i.e. moles and voles). Also by having the students take note on the number and types of prey items inside the pellet can show the diversity of the environment their particular owl lives in along with showing an energy pyramid. Having the students dissect the pellets and analyzing the bones and perhaps even reconstruct the skeleton can help students reinforce their knowledge on the skeletal system.
Questions & Answers:
1. What important information can be obtained from owl pellets?
Answer: The contents of an owl pellet can tell the observer what possible dietary preferences an animal has. Other information can include the diversity of prey species in the given habitat along with a sense of how common the prey species are.
2. Is it possible that the prey identified from the pellets does not accurately reflect the prey species population in the owls habitat? Why or why not?
Answer: There are seasonal changes in animal populations and just by analyzing one seasons worth of pellets might not be an accurate year-round representation of the population. During winter, many small mammals are provided with lots of cover in the form of snow and fallen leaves so they may have less exposure time to predators. Some animals may also just be more elusive or agile than others which will provide a harder target for capture and cause an owl to move onto a more easily accessible food source.
3. What else does an owl pellet provide besides information on what they ate?
Answer: Owl pellets provide a habitat and nursing ground for many insects and fungi. The bones and fur in the pellets provide an available food source while limiting the insects exploration which would otherwise increase exposure to predators. These insects in turn can then feed other creatures such as voles and shrews which are then preyed upon by owls thus creating a true food web cycle.
Applications to Everyday Life:
1. By reconstructing the skeleton system, students will understand the form and function of the different bones that can apply to all vertebrates. Many of the bones found in the mammals eaten by owls are similar to other animals, especially larger mammals such as humans. By analyzing the skeletons of these creatures, students can understand limitations of certain species of animals. An example of this can be by comparing the leg bones of frogs and toads and realizing frogs have larger hind limbs which cause them to jump farther when compared to the shorter legs of a toad who mostly hop or walk.
2. Students will understand the role owls and other apex predators play in maintaining the healthy ecosystem. Everything in nature is a delicate balance between organisms. When people do not understand this process and remove apex predators (i.e. lions, sharks, wolf's, etc) it can have detrimental consequences for that particular ecosystem. For example, when the gray wolf, Canis lupis, was extirpated throughout most of it's native range, the deer population exploded causing extensive damage to the native flora and causing the deer population to crash. Overfishing is another major concern since removal of many of the top predators creates an unbalance in fish populations which can prove to be an economic loss for fisherman.
3. Students will understand that the byproducts of an organism can tell the dietary story of that particular animal and/or its health. Many researchers analyze pellets or fecal matter in order to understand the complex relationships animals have in their particular habitat. Just because a person may see a particular animal eat a certain object does not mean it's diet is only composed of that object but it may in fact only contribute a small portion of its daily intake. It is also important to realize that when looking at regurgitated matter or even fecal matter that the health of the individual animal or human can be analyzed.
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