A population study of the Quokka, Setonix brachyurus Quoy & Gaimard (Marsupialia). 3. The estimation of population parameters by means of the recapture technique

Abstract

Several methods of trapping, marking, and recapturing quokkas, Setonix brachyurus, were tried, and all except a long-net sampling technique used at the summer drinking placeswereobviously unsuitable for providing data on which population studies could be based. The long-net method is described in detail and the nature of the sample obtained is discussed from the point of view of randomness. There is evidence of varying risk of capture between and within different age and sex categories. There are also indications of site avoidance within a trapping period of three consecutive nights, and of continued entry to and departure from the drinking site over the summer months. Under these circumstances the estimates of the total number of animals visiting the drinking site, and of their survival, are subject to a variety of biases. Consideration of the population composition has enabled an approximate life-table for the species to be drawn up. The general conclusion is that, owing largely to variations in natural behaviour, individual animals are not randomly caught, and that the recapture method, even when it is used in an apparently suitable situation such as this, does not provide sufficiently precise estimates of population parameters to justify the very large amount of field-work involved.