Mark and recapture

Mark and recapture is a way to figure out how many animals there are in a certain area without having to count every single one of them. Scientists catch a number of animals, mark them by putting a tag, band or some kind of marker on them, and then release them back into the wild.

After some time, the scientists go back and catch some more animals. This time, they check to see how many of the animals already have markers on them. By comparing the number of marked animals to the total number caught, the scientists can make an estimate of how many animals live in that area.

Let's say a scientist catches 10 rabbits in a field, marks them with special colored collars, and releases them back into the field. Later, the scientist comes back and catches 20 rabbits. Of those 20 rabbits, 5 have the colored collars on them.

The scientist knows that if they marked 10 rabbits and 5 of those marked rabbits were caught the second time, then they can estimate that there are about 50 rabbits in total in that field. This is because the proportion of marked rabbits to unmarked rabbits in the second catch reflects the proportion of marked rabbits to unmarked rabbits in the entire population.

Mark and recapture is a useful tool for studying populations of animals, especially those that are difficult to count or rare.