HANDS-ON ACTIVITY
Name:
ESTIMATING ANIMALS:
Mark-Recapture
In “Unlocking the Mysteries of Migration” (p. 12), you read about the millions of wildebeests, monarchs, loggerhead turtles,
and red crabs that migrate every year. But how do scientists figure out how many critters are on the move? They use several
methods to estimate animal populations. Try out the activity below to test one of these methods.
Materials:
Data Table
shoe box with lid • 1 cup each dried pinto and red
beans • 1 cup red beans
Initial Guess:
PROCEDURE:
1. Take the lid off the shoe box and empty the cup of
Number of
Number That
Total Number
Population
Sample
Captured That
pinto beans into it.
You Marked
Captured
Estimate
Were Marked
2. Look at the beans and guess how many are in the
1
box. Enter your guess in the data table (above, right).
3. Without looking, grab a handful of beans and count
2
them. “Mark” these “animals” by replacing the pinto
beans that you removed with the same number of red
3
beans. Write the number that you marked in the first
4
column of the data table.
4. Replace the lid and gently shake the box. Without
5
looking, grab another handful of beans.
5. Tally up the number of pinto beans and “marked”
Average Population Estimate:
red beans. Enter that data into the data table.
6. Use the equation (bottom, right) to estimate the
Actual Population:
population for this sample. Enter that data into the
data table.
7. Place the original pinto beans back into the box. Set the red
Total number
Number that
beans aside.
5
Population
captured
you marked
8. Repeat steps 3 through 7 four more times, entering the
Estimate =
Total number captured
data in your data table as you go. Then calculate the average
that were marked
estimate of your samples and enter that result into the data table.
9. Count the total number of pinto beans in the box and record
this in the row labeled “Actual Population.”
CONCLUSIONS
1. How did your average population estimate compare with the actual number of beans in the box?
2. With what types of habitats do you think this method of population estimation would work best?
3. What do you think would happen if you were to repeat steps 3 through 7 five more times and average the results with
that additional data?
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