Activity: Estimating population size

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Activity: Estimating population size

Mark and Recapture

In this procedure, biologists use traps to capture the animals alive and mark them in some way. The animals are returned unharmed to their environment. Over a long time period, the animals from the population continue to be trapped and data are taken on how many are captured with tags. A mathematical formula is then used to estimate population size.


Measure one cup of dried beans. Put them in a larger container.

Capture 15 “animals” by removing them randomly from the container.

Place a mark on them using a permanent marker.

Return the 15 marked “animals” to the container.

With your eyes closed, grab a handful of the population. This is the recapture step. Record the number of “animals” recaptured in total and the number that have a mark on them on the data table.

Return the “animals” to the container and repeat. Do 10 recaptures.

Average the “Number Captured” and “Number Recaptured with mark.” Use these numbers in your calculations.

When the ten recaptures are completed, enter the totals on the data table.

Calculations = Find your Population Estimate

Population Estimate = (Total number captured) X (Number marked initially {15})

(Total Number Recaptured {Marked})

Estimated Size ___________

Example: Capture 27, 3 have marks

Population Estimate= (27) X (15)


Estimated Size: 135

Count the number of beans (animals) in your population.

To receive credit, fill in attached pdf sheet, save it as a new document on your computer, then upload it. Check to make sure it saved WITH data