This is a method used to estimate a population size. Populations can be difficult to sample because species move around all of the time.
Capture-recapture work as follows:
1. A trap is used to catch a sample of individuals, e.g. mice.
2. The sample is counted, recorded and each individual is marked with a numbered tag/band or a dot of paint.
3. The individuals are released unharmed back into the environment, and are given time to redistribute themselves among the unmakred population.
4. Another sample of individuals is captured Some of them are already marked, some arent.
5. The unmarked animals are counted and recorded. They are then marked and released.
This formula can thne be used to estimate the total population size in the habitat: