The method we will focus on today is the Lincoln - Peterson Method . This method was originally designed to estimate fish and bird populations, but today is used for a wide variety of animals. How this method works is that a number of individuals in a population are captured and marked in some way that is identifiable and then released. When animals are marked, precautions are made to use methods that will not harm the animal in any way or that would jeopardize its chances of survival once released again. After several days, marked animals have had a chance to mix back into their original population.
Investigators then capture another sample of animals.
Captured animals are counted and the number that are marked, as well as those that are not marked, are recorded. It is expected that if the population is large there would be relatively few animals recaptured. On the other hand, in a small population there should be a large number of animals recaptured. The following equations indicate that the ratio of the total population to the number of animals marked on the first date is equal to the ratio of the number caught on the second date to the number that were recaptured on the second date. This equation can be rearranged using simple algebra to the following equation.