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

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.

Female White-tailed Deer Survival Across Ecoregions in Minnesota and South Dakota

“…We speculate that limited availability of forested cover in grassland regions of the Northern Great Plains may interact with severe winter weather and subsequently increase natural mortality (Brinkman et al, 2004). Deer in these habitats initiate long-distance migrations to locate suitable cover and forage habitats (Grovenburg et al, 2009), presumably increasing energy expenditure for maintenance and locomotion DePerno et al, 2000).…”

“…In grassland regions, permanent escape cover (i.e., forested cover) often is limited and highly fragmented (Smith et al, 2002). Deer are forced to make longer movements (Grovenburg et al, 2009) across open areas, possibly leaving them vulnerable to hunters. In intensively farmed areas, well-established road networks and high hunter density may help explain greater human-related mortality (Hansen et al, 1997;Brinkman et al, 2004;Grovenburg et al, 2008).…”

“…We captured adult ($18 mo at capture) and yearling (6-18 mo at capture) female whitetailed deer using helicopter net-guns (Jacques et al, 2009) in DAE during Jan. 2000-2003, in WCBPE during Jan. 2003and in NWGPE during Apr. 2005and Jan. 2006.…”

The use of box-traps for wild roe deer: behaviour, injuries and recaptures

“…Typically, capturing wild animals causes stress and can potentially cause injuries, behavioural and physiological disorders and in some cases death (Arnemo et al 2006;Iossa et al 2007). To date several different methods have been used to capture different deer species such as drive nets (roe deer; Morellet et al 2009), net guns (whitetailed deer; Jacques et al 2009), remote drug delivery by darting (moose; Arnemo et al 2006), netted cage traps (white-tailed deer; VerCauteren et al 1999), drop-nets (mule deer;D'Eon et al 2003), cannon nets (Hawkins et al 1968), corrals (Rempel and Bertram 1975) and box-traps (roe deer; Heurich et al 2012). Several variables should be taken into consideration when decisions about which capture and handling methods are used, as some methods are not suitable in adverse weather conditions, in differing habitat types and population sizes.…”

“…Various studies examine behavioural effects on captured animals by assessing alterations in movement, habitat choice and search for cover after being released (Jacques et al 2009;Morellet et al 2009). Behavioural analyses can generate useful information about expected injuries, indicating why and when these are likely to occur.…”