This is a method of tracking members of a population. A random sample of individuals in a population is captured, tagged and released. Once the tagged members mix back with the population (days or weeks), the population is again sampled.

Mark - Recapture

This is a method commonly used in ecology to estimate the animals in the population. A portion of the poplation is captured, marked and released. Another part of the population will later on be captured. This can be used to estimate the population in an assumption that the portion that was captured is proportional to the entire populatio. This is obtained by dividing the number of marked individual by the individual marked on second capture. This is one of the simples and most practical method of estimating population,