2.1. Censusing a whole populationThis method works only if organisms can be easily observed, their numbers are not too big, and the area is well bounded and is not too large. Examples: trees in a small isolated forest; all bird nests are censused in the New-York state (see Pielou 1977).
Migrating populations can be counted using aerial photography. This method is used when the population has seasonal migration. Examples: sandhill cranes and caribou.