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Development and Evaluation of Sightability Models for Summer Elk Surveys

Charles R. Anderson, Jr., David S. Moody, Bruce L. Smith, Frederick G. Lindzey and Robert P. Lanka
The Journal of Wildlife Management
Vol. 62, No. 3 (Jul., 1998), pp. 1055-1066
Published by: Wiley on behalf of the Wildlife Society
DOI: 10.2307/3802558
Stable URL: http://www.jstor.org/stable/3802558
Page Count: 12
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Development and Evaluation of Sightability Models for Summer Elk Surveys
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Abstract

We developed 2 sightability models from summer helicopter surveys of radiocollared elk (Cervus elaphus) in Grand Teton National Park, Wyoming. Significant variables (P < 0.05) included elk group size, activity, and percent vegetation cover for Model A, and elk group size and percent vegetation cover for Model B. We compared these 2 summer models and a winter elk sightability model developed in Idaho that incorporates group size, percent vegetation cover, and percent snow cover. We based model comparisons on predicted detection rates and model performance when applied to well-documented elk populations at Starkey Experimental Forest and Range, Oregon (SEF), and Wind Cave National Park, South Dakota (WCNP). Predicted sightability was similar from summer Models A and B for active elk in <60% vegetation cover, but was lower from Model A for bedded elk. Model estimates of elk abundance (WCNP, SEF) and composition (SEF) usually were more accurate and consistently more precise from Model B, suggesting elk activity had little influence on estimates of summer elk population characteristics. Comparisons between Model B and the Idaho model indicated predicted sightability of small groups (≤10 elk) was similar; the Idaho model provided better accuracy and precision for validation tests of populations consisting of predominantly small elk groups (WCNP: = 4.7 elk/group; SEF: = 6.3 elk/group). The Idaho model, however, overestimated detection of large elk groups (30-45 elk/group) in moderate-dense vegetation (>30% vegetation cover), but this overestimation was accounted for by Model B. Thus, we recommend application of the Idaho model during summer surveys where elk are less gregarious (<20 elk) and recommend application of summer Model B to high-density elk populations where elk occur in larger groups.

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