Evaluating Ungulate Mortality Associated With Helicopter Net‐Gun Captures in the Northern Great Plains

Abstract

ABSTRACT Ungulate mortality from capture‐related injuries is a recurring concern for researchers and game managers throughout North America and elsewhere. We evaluated effects of 7 variables to determine whether ungulate mortality could be reduced by modifying capture and handling procedures during helicopter net‐gunning. During winter 2001–2006, we captured 208 white‐tailed deer (Odocoileus virginianus) and 281 pronghorn (Antilocapra Americana) by helicopter net‐gunning throughout the Northern Great Plains. Of 281 pronghorn, 25 (8.9%) died from capture‐related injuries; 12 were from direct injuries during capture, and 13 occurred postrelease. Of 208 deer, 3 (1.4%) died from injuries sustained during helicopter captures, with no mortalities documented postrelease. We used logistic regression to evaluate the probability that ungulates would die of injuries associated with helicopter net‐gun captures by analyzing effects of snow depth, transport distance, ambient and rectal temperatures, pursuit and handling times, and whether individuals were transported to processing sites. The probability of capture‐related mortality postrelease decreased 58% when transport distance was reduced from 14.5 km to 0 km and by 69% when pursuit time decreased from 9 minutes to <1 minute. Wildlife managers and researchers using helicopter capture services in landscapes of the Midwest should limit pursuit time and eliminate animal transport during pronghorn and white‐tailed deer capture operations to minimize mortality rates postrelease.