On the reliability of enumeration for mark and recapture census of voles

Abstract

Some studies of populations in small rodents rely on enumeration of individuals to provide an estimate of population size. A computer simulation of the capture–recapture process was used to examine the influence of five population parameters on the reliability of enumeration. Enumeration is shown to be insensitive to population size, survival between sampling intervals, and individual variation in the probability of capture. Enumeration is sensitive to the probability of capture; if the probability of capture for the average individual falls below 0.5, the enumeration technique provides a poor estimate of population size. Enumeration is also extremely sensitive to reduced probabilities of capture for unmarked animals. Data from capture–recapture studies of five species of Microtus were used in the computer simulation, and it was concluded for these five species that enumerated populations are at least 10–20% smaller than the actual populations.