A mark–recapture technique, devised in the 1950s by N. T. J. Bailey, for estimating the size of an animal population in which a sample of animals is caught, marked, and released. This procedure is followed on two subsequent occasions. Provided each sample contains more than 20 individuals, the population estimate (P) is given by (a2n2r4)/r1r3, where a2 is the number of marked individuals released from the second catch, n2 is the number caught in the second sample, r4 is the number of individuals in the third catch that were marked in the first catch, r1 is the number of individuals marked in the first catch that were caught in the second, and r3 is the number of individuals caught in the third sample that were marked in the second. If the sample numbers fewer than 20 individuals, an adjustment is made, giving: P=(a2(n2+1)r4)/(r1+1)(r3+1).
Subjects: Zoology and Animal Sciences — Ecology and Conservation.