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Wednesday, February 8 • 8:00am - 8:20am
Technical Session. Double Observer Evaluation of Pronghorn Aerial Line Transect Surveys

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AUTHORS: Timothy J. Smyser, University of Idaho; Richard J. Guenzel, Wyoming Game and Fish Department; Christopher N. Jacques, Western Illinois University; and Edward O. Garton, University of Idaho

ABSTRACT: Comparisons of pronghorn (Antilocapra americana) population estimates derived from quadrat sampling from helicopters versus distance sampling (DS) from fixed-wing suggest that DS underestimates density, likely due to violations of the critical assumption of DS that all pronghorn within the innermost distance band (nearest to the aircraft) are detected. We sought to rigorously test this critical assumption by applying independent, paired observers to an established distance sampling protocol. Additionally, we evaluated effects of cluster size, landscape composition, and observer position (front versus rear seat) on the probability of detection. We used mark-recapture distance sampling (MRDS) analysis techniques to explicitly estimate detection probability for pronghorn in the innermost distance band. We compared density estimates produced by MRDS with those produced by multiple covariate distance sampling (MCDS), a method that assumes complete detection for clusters on the transect line. We identified violations of the assumption that all clusters within the innermost distance band were detected, which would contribute to proportional biases in density estimates for analyses that assume complete detection. The frequency of missed clusters within the innermost distance band was modest (4%) for observers in the front seat. In contrast, the frequency of missed clusters was more substantial (21%) for observers in the rear seat. Further, cluster size and landscape composition influenced pronghorn sightability. Paired observers allowed us to quantify and correct for the bias caused by the failure to detect all pronghorn within the innermost distance band. Monitoring programs should incorporate paired observer validation trials to quantify the frequency of missed clusters within the innermost distance band under typical survey conditions. Managers can improve the precision of pronghorn aerial line transect surveys by incorporating cluster size and landscape composition into detection models without incurring additional survey costs.

Wednesday February 8, 2017 8:00am - 8:20am
Grand Ballroom C

Attendees (5)