Estimates of the size of winter flocks of the Pied Currawong, Strepera graculina (Shaw) from mark -recapture data - a new approach

Abstract

Banding records were used to estimate the size of non-breeding winter flocks of the pied currawong, Strepera graculina, at Albury, N.S.W., during 1964 and 1965. A new method of analysing mark-recapture data is compared with conventional methods, and it is shown that the flocks contained between 500 and 1000 birds in both years. In 1964, the new method provided information on emigration and immigration that was not apparent when the data were treated in the conventional way. The new approach considers the common situation in which a population (flock) is sampled continuously by catching one member (bird) at a time, marking (banding) it, and returning it to the population. For closed populations, the population size was estimated by a method involving cumulative catch and recapture data. Subsequently, this method was successfully tested by simulating the sampling of 20 "populations" of 10,000 random numbers with a computer. The method also provided a simple way of controlling sampling effort based on recapture data to obtain any desired precision in the estimation of population size.