Quadrats are only suitable for measuring abundance of animals if they are very slow moving and small.

The mark-release-recapture technique is a method used to estimate the abundance of motile animals by catching, marking, and releasing a known number of animals.

Later, another sample is collected and the number of marked individuals is recorded.

1. Marked individuals distribute evenly
2. The population has a definite boundary
3. There are few deaths or births, and little emigration or immigration
4. Marking is non-toxic and does not increase predation risk
5. Marks are not lost

1. Capture as many individuals as possible in a sample area
2. Mark or tag each individual
3. Release the marked animals back into the sample area
4. Allow time for them to redistribute throughout the habitat
5. Recapture as many individuals as possible in the original sample area
6. Record the number of marked and unmarked individuals present in the sample
7. Input the values recorded into a formula to estimate the population size

If the marking makes the individual more noticeable, it may increase its risk of predation.

This could affect the accuracy of the population estimate.

If the mark or label is lost or rubbed off, the individual may not be identified as a marked individual when recaptured, which could affect the accuracy of the population estimate.

If marked individuals do not distribute evenly, then the second sample would not be representative of the whole population.

Deaths and births could change the total population size, affecting the accuracy of the population estimate.

If the population doesn't have a definite boundary, this could change the total population size and affect the accuracy of the population estimate.

If the marking is toxic, it could harm or kill the individual.

This could affect the accuracy of the population estimate.