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Counting Animal Populations

Grades: 5-8
Author: Joyce Brumberger
View Student Lesson Plan


Module Description

As a result of the professional development provider-conducted module, participants will learn about the method that field scientists use to determine the population of a species for a specified study area. Through collaboration they will design their own strategic method for counting the population of students in their school. Participants will design a lesson they can implement in their own classroom.


  • Participants will learn vocabulary terms such as abiotic and biotic.
  • Participants will learn how the Mark and Capture system for population studies is conducted.
  • Participants will be able to calculate estimated populations using a simple mathematical formula.
  • Participants will be able to design a method of counting the population of students in their school.
  • Participants will produce a lesson plan to guide their own students in the design and implementation of a Mark and Capture study.


  • 3 large jars of equal size
  • Suggested jar contents: M&M's, large jelly beans, gum drops
  • Post-it Notes

For each group:

  • 1 1000 mL beaker
  • 1 500 mL beaker
  • Black beans, enough to fill the 1000 mL beaker 1/2 full
  • White beans, enough to fill 500 mL beaker 1/2 full
  • 1 quart size plastic container
  • Aluminum foil squares to cover top of 1000 mL beaker
  • Large rubber bands to hold aluminum foil in place
  • Baking sheet or other large flat container
  • Data Table Worksheet - 1 for each participant



  1. Display the three clear jars containing the M&M's, large jelly beans, and gum drops.
  2. Instruct participants to estimate the number of gum drops in the jar and record their estimate and name on a Post-it note.
  3. Instruct participants to post their answers in the Gum Drop column on the board by placing their answer so that the numbers increase in a descending order. Post-it notes may have to be shifted to properly place an estimate in the correct place.
  4. Once all the estimates are posted, reveal to the group the correct number of gum drops. If no one guessed the exact amount, ask the group to help determine which estimate was closest to the actual number, which could be higher or lower than the actual value.
  5. Recognize the winner(s) with a round of applause.
  6. Instruct participants that they will have the opportunity to estimate again, this time with the jelly beans.
  7. Repeat steps 2-5.
  8. With the knowledge gained from previous estimates, tell participants that they will be given one last opportunity to estimate.
  9. Repeat steps 2-5

Assessment: Assessment is ongoing as participants respond orally and with written estimates during the Engagement phase. Improvement in estimating ability for succeeding jars can be noted for each individual.


  1. Divide participants into groups of three.
  2. Tell participants that the black beans in the jar represent an animal species in the wild and that the beaker represents the study area in which the animals live.
  3. Instruct participants that they are going to conduct two "capture and release" events.
  4. Brainstorm with participants what some of the assumptions are that wildlife managers make when doing a population study. The assumptions are:
    • no animals ran out of the study area - emigration
    • no new animals enter into the study area - immigration
    • there were no births - natality
    • there were no deaths - mortality
    • animals did not become "trap happy" - looked for the traps
    • animals did not become "trap shy" - ran away from the traps
  5. Instruct participants that without looking, one member of the group (the trapper) will reach into the beaker of black beans (the critters) and remove a handful of beans. This is considered the "first trapping".
  6. Instruct all members of the group to count the # of captured beans and record it on their data tables.
  7. Tell participants that to save time marking each captured bean, that they should replace it with one of the white beans. All captured black beans should be replaced 1:1 with the white beans. White beans represent a tagged animal that was captured and released.
  8. Instruct participants to put the black beans that were exchanged for white beans in the plastic container.
  9. Instruct participants to put the white beans back in the 1000 mL beaker.
  10. Tell participants to cover the beaker with aluminum foil and secure with a large rubber band.
  11. Instruct participants to securely hold the aluminum foil and vigorously shake beaker until the beans are dispersed evenly.
  12. Instruct participants that the trapper should once again reach into the beaker, without looking, and remove a handful of beans.
  13. Instruct participants to separate the beans (critters) into a pile of white beans (which were captured again) and a pile of black beans (critters that were captured for the first time during the second event.) Count and record the # of white and black beans separately in the data table. Add both values to determine a total and record.
  14. Instruct the participants to estimate the population size using the formula below and record. N = total estimated population

N total estimated population = ((total captured in first trapping) x (total captured in second trapping)) / (number of marked recaptured)

Sample Data and Calculation



# Black Beans

# White Beans Recaptured

# Marked Animals

Total Captured





First Trapping










Second Trapping








N total estimated population = ((total captured in first trapping) x (total captured in second trapping)) / (number of marked recaptured)

N = (89 x 93) / 37 = 223.7 = 224

  1. Instruct participants to record their calculated population estimate in the data table.
  2. Instruct participants to remove the white beans from the 1000 mL beaker, place them back into the 500 mL of white beans, and return the black beans from the plastic container to the 1000 mL beaker.
  3. Instruct participants to repeat the mark and recapture technique two (2) more times.
  4. Instruct participants to calculate "N" for each trial and record.
  5. Instruct participants to calculate the average population size and record.
  6. Instruct participants to remove the white beans from the 1000 mL beaker and return the black beans from the plastic container to the 1000 mL beaker.
  7. Tell participants to carefully empty black beans onto a baking sheet and count the total number of beans to determine the actual population size.
  8. Instruct participants to calculate the percent error of their study using the formula

Percent Error = Actual Population - Calculated Average x 100

Actual Population

Assessment: Assessment is ongoing as participants partake in the exercise counting beans and orally discussing findings and recording on worksheet.


  1. Ask participants to relate their experiences when estimating the objects in the jar. Answers will vary, but responses may indicate that as they gained experience with estimating, their accuracy improved.
  2. Ask participants what is the value of estimating. Answers will vary, but the value of estimating allows individuals to determine a quantity without having to count the actual number.
  3. Ask participants what are some ways that estimates can be made. Responses may be that estimates can be made based on visual observations and past experience and/or visual observations and a mathematical formula to help calculate a value.
  4. Ask the participants what factors affected the changes in their total estimated populations for each trial? Most commonly the response is that handful sizes were very inconsistent.
  5. Review with participants the assumptions that were made at the beginning of the exploration.
    1. no animals ran out of the study area - emigration
    2. no new animals enter into the study area - immigration
    3. there were no births - natality
    4. there were no deaths - mortality
    5. animals did not become "trap happy" - looked for the traps
    6. animals did not become "trap shy" - ran away from the traps
  6. Studies can be conducted using a "closed" system or an "open" system. Ask participants to identify the type of system modeled in the Exploration phase. Closed
  7. Ask participants to give an example of a study that might actually be conducted in a closed system. Answers will vary, but one example is the study of a deer population in which an area of many square acres is fenced.
  8. Ask participants to post their percent error on the board or a poster board. Ask participants to indicate along side their percentage value whether they took large or small handful samples.
  9. Ask participants to analyze the data posted to determine if any correlations or explanations could be made. Commonly, those who took small handfuls had a larger percent error than those with larger samples. This exemplifies that in science many repetitions of an experiment or a study conducted with large populations result in more accurate information.
  10. Discuss with participants the terms abiotic and biotic. Abiotic factors refer to the non-living physical conditions that affect organisms. Examples are temperature, water, soil, climate, sunlight, pH, wind, and oxygen. Biotic factors refer to the interactions among organisms. Examples are an organism's response to the available food supply or competition for space with its own species or another.
  11. Ask participants what information a population study could provide? Along with the natural fluctuation of populations of species, the study of a specific specie population can help assess environmental conditions. These plant or animal organisms are referred to as "indicator" species because of their low range of tolerance to a specific environmental factor. Lichens are very sensitive to toxic gases and are used to study air pollution. Frogs have very sensitive skin. The development of skin diseases or disorders in large populations reflects changes in UV radiation levels.

Assessment: Participants' oral explanations of their data, analysis and conclusion will provide the professional development provider the ability to evaluate participants understanding of these aspects of experimentation.


  1. Working in pairs, instruct participants to design a method for calculating the total number of students in their school for the grade they teach.
  2. Instruct participants that their design must be clearly outlined and age appropriate.
  3. Ask each set of partners to share their design strategies with the whole group.


The sustainability of an ecosystem is a function of the delicate balance between abiotic and biotic factors. Animal populations rise and fall over time based on the degree these factors shift. Slight changes in air or water temperature, for example, could dramatically impact animals with a narrow range of tolerance. A fluctuation in food supply, a biotic factor, could increase or decrease the population of a species.

We commonly hear or read statistics about animals that are put on the threatened or endangered species lists. How is the total population of a species determined? Understanding the concept of sampling and the application of simple mathematics in which to analyze the data, teachers will be better equipped to impart to their students how population studies are conducted and how this information can be effectively used.

Science Standards

As a result of activities in grades 5-8, all participants should develop an understanding that

  • General abilities, such as systematic observation, making accurate measurements, and identifying and controlling variables should be developed. They should also develop the ability to clarify their ideas that are influencing and guiding the inquiry, and to understand how those ideas compare with current scientific knowledge. Participants can learn to formulate questions, design investigations, execute investigations, interpret data, use evidence to generate explanations, propose alternative explanations, and critique explanations and procedures.
  • Thinking critically about evidence includes deciding what evidence should be used and accounting for anomalous data. Specifically, participants should be able to review data from a simple experiment, summarize the data, and form a logical argument about the cause-and-effect relationships in the experiment. Participants should begin to state some explanations in terms of the relationship between two or more variables.
  • With practice, participants should become competent at communicating experimental methods, following instructions, describing observations, summarizing the results of other groups, and telling other participants about investigations and explanations.
  • Mathematics is essential to asking and answering questions about the natural world. Mathematics can be used to ask questions; to gather, organize, and present data; and to structure convincing explanations.

As a result of their activities in grades 5-8, all participants should develop understanding of:

  • A population consists of all individuals of a species that occur together at a given place and time. All populations living together and the physical factors with which they interact compose an ecosystem.

NSES CONTENT STANDARD F: Science in Personal and Social Perspectives
As a result of activities in grades 5-8, all students should develop understanding of

  • When an area becomes overpopulated, the environment will become degraded due to the increased use of resources.
  • Causes of environmental degradation and resource depletion vary from region to region and from country to country.

NSES PROFESSIONAL DEVELOPMENT STANDARD A: Professional development for teachers of science requires learning essential science content through the perspectives and methods of inquiry. Science learning experiences for teachers must:

  • Involve teachers in actively investigating phenomena that can be studied scientifically, interpreting results, and making sense of findings consistent with currently accepted scientific understanding.
  • Address issues, events, problems, or topics significant in science and of interest to participants.
  • Introduce teachers to scientific literature, media, and technological resources that expand their science knowledge and their ability to access further knowledge.
  • Build on the teacher's current science understanding, ability, and attitudes.
  • Incorporate ongoing reflection on the process and outcomes of understanding science through inquiry.
  • Encourage and support teachers in efforts to collaborate.

NSES PROFESSIONAL DEVELOPMENT STANDARD B: Professional development for teachers of science requires integrating knowledge of science, learning, pedagogy, and students; it also requires applying that knowledge to science teaching. Learning experiences for teachers of science must:

  • Connect and integrate all pertinent aspects of science and science education.

Best Teaching Practices

  • Learning Cycle
  • Science Process Skills
  • Inquiry

Time Frame

Engagement: 20 minutes

Exploration: 60 minutes

Explanation: 20 minutes

Exploration: 30 minutes



  1. Count the number of objects that are placed in each of the three jars and record quantities.
  2. Prepare the board or a poster board with three columns. Label one column for each jar's content.

Exploration: For each group

  1. Fill the 1000 mL beaker 1/2 full with black beans.
  2. Fill the 500 mL beaker 1/2 full with white beans.
  3. Cut squares of aluminum foil to fit over the 1000 mL beaker with enough to hang over the sides to be secured with a rubber band.





Explanation of Science

One of the most difficult jobs for a wildlife manager is to accurately determine the size or density of a population. Because of the intrinsic difference in life cycles between plants and animals, wildlife managers have developed techniques for counting each group. Plants can be simply counted and reported as so many individuals per square meter or hectare. On the other hand, animals are more difficult to count due to their mobility.

Wildlife managers use a "Mark and Recapture" technique for counting animals. For this method to yield effective results (good population density values), several assumptions need to be considered and controlled. The assumptions are that:

  1. no animals ran out of the study area - emigration
  2. no new animals enter into the study area - immigration
  3. there were no births - natality
  4. there were no deaths - mortality
  5. animals did not become "trap happy" - looked for the traps
  6. animals did not become "trap shy" - ran away from the traps

The assumption, therefore, is that the population being counted is considered static - neither growing, nor declining or being stressed by the inventory procedure. Managers know this is not realistic; consequently, they adjust their values based on the natural history of the organisms and a formula to calculate the population referred to as the Lincoln Petersen method of analysis.

N total estimated population = ((total captured in first trapping) x (total captured in second trapping)) / (number of marked recaptured)


Counting Animal Populations Data Table


Research how the spread of diseases through a population is studied and determined.

Analyze graphs reflecting the fluctuation of particular species population in a given period of time to propose explanations for the occurrence.

Explore the history of marine animal populations at to learn the factors that affected populations over centuries.

Select an animal on the threatened or endangered species list and research the factors that are affecting the decline of the population. Explore the work being done, if any, to preserve the population.

Explore other methods of counting animal populations, such as migratory birds.

Lesson Implementation Template

Download Lesson Implementation Template: Word Document or PDF File


Try to group participants heterogeneously with diversity in mind. Encourage all members of the group to participate in counting and recording their data.


None available for this module.