Animal Population Census

the determination of the number of animals inhabiting a given area, both on land and in a body of water. The census may be absolute, that is, all individuals in a given area are counted, or relative, that is, only a certain number of individuals are counted and the total number remains unknown. The latter type is more feasible and therefore generally used. Relative-absolute conversion factors exist, obtained by comparing the absolute and relative censuses for similar areas. In a number of cases where only a relative census has been taken, it is possible to estimate the absolute number of animals using the conversion factors.

The techniques of counting animals differ, depending on the kind of animal. Thus, the number of small plankton and soil animals is analyzed in specific amounts of water or soil samples obtained by special instruments. The number of flying insects, fish, and small rodents is determined by the number of individuals caught in a trap in a given time period. The number of birds, reptiles, and mammals is determined by the number of individuals encountered and the number of nests and dens in a given area; during the winter the population of many mammals is determined by the number of tracks.

An animal population census makes it possible to determine the adherence of animals to specific habitats, identify rhythms in animal activities, determine the nature of seasonal and annual changes in population size and the factors that influence them, and clarify other aspects of animal ecology. Animal population censuses are useful in organizing pest control, limiting the taking of commercial animals, and determining the biomass of individual species and the total productivity of biological communities.