Evaluation of a Mark-Resighting Technique for Woodland Caribou in Newfoundland

The authors evaluated properties of the Petersen mark-resight technique for estimating the population size of 6 woodland caribou (Rangifer tarandus) herds in Newfoundland. The authors' objective was to determine the robustness and efficiency of a novel marking technique for estimating population size of caribou where sightability bias is marginal. We marked caribou with pressurized oil-alkyde paint applied from a helicopter. Resighting surveys were conducted 2-3 weeks later. Data from 15 radiocollared animals indicated populations were closed and marks were not lost. The probability of resighting a marked individual was independent of group size, which indicated heterogeneity in sighting probabilities had a marginal effect on the reliability of population estimates. Thus, most of the fundamental assumptions of the Petersen estimate were supported. Although the authors could not assess accuracy of this method, the degree of precision was dependent primarily on the number of marked animals resighted. Increasing the initial number of marked individuals did not significantly reduce the width of confidence intervals unless the total number of animals resighted also was increased. However, due to the efficiency of marking many animals in a short period, more effort can be allocated to resighting surveys without increasing costs. We believe this technique should provide a cost-effective method for obtaining precise population estimates of woodland caribou and other large mammals where sightability bias is low.