Other abundance measuring techniques do not work on animals as they move around, and also are difficult to find.
Method
A number of animals are caught, marked then released back into the wild. Later, you randomly collect another group of animals, and count the number which were marked.
estimated population = no. in 1st sample x no. in 2nd sample/ no. of marked recaptured
Assumptions
- the marked animals distribute themselves randomly among the rest of the population.
- there is no immigration, emmigration, birth or death in the population
- the mark isn't lost before recapture
- the marking doesn't increase the probability of death (i.e. isn't toxic, or makes them more likely for predation)
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