Abstract

Counts from a helicopter of known numbers of marked (radio-collared) and reasonably well known numbers of unmarked mule deer (Odocoileus hemionus hemionus) in 4 58-70-ha pastures were used to calculate 114 Lincoln-Petersen estimates of population size. Three approaches to combine Lincoln-Petersen estimates were explored: simple arithmetic mean, median, and joint hypergeometric maximum likelihood. Compared to individual estimates, all 3 produced narrower confidence intervals and increased the percentage of confidence intervals that covered true population values. The median was least sensitive to outliers, but the joint hypergeometric maximum likelihood provided -40% smaller confidence intervals. About the same percentage of confidence intervals for all 3 estimators (64-73%) overlapped at least part of the ranges of true population size. For all 3 estimators, a large proportion (>45%) of a small population should be marked to obtain more reliable estimates and greatest confidence interval coverage. However, there is still high probability that mean population estimates will be low. J. WILDL. MANAGE. 51(1):41-46 Testing Petersen's mark-recapture method (Petersen 1896, Lincoln 1930) using aerial sampling has received scant attention with regard to big game population estimates. Woolf (1973) used the technique to estimate size of a confined white-tailed deer (0. virginianus) population in Pennsylvania, and Rice and Harder (1977) initially evaluated the technique with known numbers of confined white-tailed deer in Ohio. To our knowledge, research to assess accuracy of the technique to estimate size of mule deer populations is lacking. During tests of aerial counting accuracy with mule deer in fenced enclosures (Bartmann et al. 1986), considerable numbers of unmarked deer were present along with radio-collared deer that were stocked, thus presenting a unique opportunity to test aerial mark-recapture estimation procedures. In the experimental protocol used in this study, animals are marked with radio collars so that the number of marked animals in an area can be determined with biotelemetry prior to an aerial survey. Since unmarked animals sighted during an aerial survey are not marked (radio-collared) for subsequent surveys, the Schnabel-Darroch multiple recapture protocol (Model M, of Otis et al. 1978) is not applicable for this situation. Rather, multiple applications of the Lincoln-Petersen estimator are computed where the initial marking (radio collaring) of animals constitutes the 1st sample, and the numbers of marked and unmarked animals counted during the aerial survey provide the 2nd sample. Each aerial survey then produces a new Lincoln-Petersen estimate. Our objective in this paper is to evaluate performance of 3 procedures (simple arithmetic mean, median, and joint hypergeometric maximum likelihood estimate) to combine repeated Lincoln-Petersen estimates using aerial markrecapture data where total numbers of deer were reasonably well known. This research was funded by Colo. Fed. Aid Wildl. Restor. Proj. FW 26P, and by the U.S. Dep. Energy, Contract W-4305-36 to Los Alamos Natl. Lab. and DE-FG02-85ER60297 to Colorado State Univ. We thank D. R. Anderson for critically reviewing the manuscript. STUDY AREA AND METHODS Four contiguous 58-70-ha pastures on pinyon pine (Pinus edulis)-Utah juniper (Juniperus osteosperma) winter range in Piceance Basin, northwestern Colorado, were stocked with a total of 48 mule deer in November and December 1983. Each deer was fitted with a radio transmitter mounted on a white collar 5.1 cm wide. Deer were not marked for individual identification during aerial surveys, as this was 1 Present address: Department of Fisheries and Wildlife, University of Minnesota, St. Paul, MN 55108.

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