recaptura

Recaptura is the act of capturing an animal, object, or person that has been captured previously, typically as part of a study or control effort. In scientific contexts, the term is closely associated with mark-recapture or capture-recapture methods, used to infer quantities that are difficult to measure directly, such as population size, survival, or movement.

In ecology and wildlife management, the basic approach involves capturing a sample of individuals, marking or tagging them, releasing them back into the wild, and then conducting one or more subsequent capture occasions. The data from the initial capture (the number marked), the size of the second sample, and the number of recaptured marked individuals are used to estimate the total population. A common simple estimator is N ≈ (n1 × n2) / m, where n1 is the first capture size, n2 is the second capture size, and m is the number of recaptured marked individuals. More complex models, such as Schnabel’s estimator or the Jolly-Seber model, address multiple samples and open populations.

Key assumptions include a closed or well-characterized population between sampling events, marks that are not lost or overlooked, and equal catchability among individuals. Violations can bias results, especially if marked individuals alter their capture probability (trap-shyness or trap-happiness) or if mortality and migration occur.

Beyond ecology, recaptura methods have been applied to estimate sizes of hard-to-count human or animal populations in epidemiology and social sciences, such as hidden or stigmatized groups, by leveraging repeated capture and marking data.

See also capture-recapture.