Christopher C. Swanson

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.

Survival of White-Tailed Deer Neonates in Minnesota and South Dakota

ABSTRACT Understanding the influence of intrinsic (e.g., age, birth mass, and sex) and habitat factors on survival of neonate white-tailed deer improves understanding of population ecology. During 2002–2004, we captured and radiocollared 78 neonates in eastern South Dakota and southwestern Minnesota, of which 16 died before 1 September. Predation accounted for 80% of mortality; the remaining 20% was attributed to starvation. Canids (coyotes [Canis latrans], domestic dogs) accounted for 100% of predation on neonates. We used known fate analysis in Program MARK to estimate survival rates and investigate the influence of intrinsic and habitat variables on survival. We developed 2 a priori model sets, including intrinsic variables (model set 1) and habitat variables (model set 2; forested cover, wetlands, grasslands, and croplands). For model set 1, model {Sage-interval} the lowest AICc (Akaikes information criterion for small sample size) value, indicating that age at mortality (3-stage age-interval: 0–2 weeks, 2–8 weeks, and >8 weeks) best explained survival. Model set 2 indicated that habitat variables did not further influence survival in the study area; &bgr;-estimates and 95% confidence intervals for habitat variables in competing models encompassed zero; thus, we excluded these models from consideration. Overall survival rate using model {Sage-interval} was 0.87 (95% CI = 0.83–0.91); 61% of mortalities occurred at 0–2 weeks of age, 26% at 2–8 weeks of age, and 13% at >8 weeks of age. Our results indicate that variables influencing survival may be area specific. Region-specific data are needed to determine influences of intrinsic and habitat variables on neonate survival before wildlife managers can determine which habitat management activities influence neonate populations.

Selenium Status and Antibodies to Selected Pathogens in White- tailed Deer (Odocoileus virginianus) in Southern Minnesota

To determine exposure to a variety of infectious diseases potentially important for native ungulates, livestock, and humans, serum samples from 114 (94 adults, 20 fawns) female white-tailed deer (Odocoileus virginianus) were collected during January 2000–03 from multiple locations in southeast (SE) and southwest (SW) Minnesota. Antibody prevalence was determined for the following pathogens: Mycobacterium avium subsp. paratuberculosis, Leptospira interrogans (six serovars), Anaplasma marginale, Borrelia burgdorferi, Brucella abortus, epizootic hemorrhagic disease virus, and bovine viral diarrhea virus (BVDV) types 1 and 2. Samples collected in 2001 were screened for antibodies against Anaplasma phagocytophilum, and whole blood was submitted for polymerase chain reaction (PCR) testing for A. phagocytophilum and B. burgdorferi. In addition, serum selenium concentrations were evaluated for samples collected during 2001– 03. Antibody prevalence and selenium concentration were compared by age-class and geographic region. Antibodies to all of the infectious agents except A. marginale and B. abortus were detected; when detected, antibody prevalence was highest in adults. Deer collected from SE Minnesota had a higher antibody prevalence to B. burgdorferi than SW deer. Blood culture and PCR results for A. phagocytophilum and B. burgdorferi were negative. Antibodies against BVDV (combined types 1 and 2) were more prevalent (χ2=3.617, P≤0.029) in deer collected in SW (41%) than in SE (25%) Minnesota. No statistically significant differences in serum selenium concentrations were detected when data were analyzed by age-class or by geographic location.

Aggressive Defensive Behavior by Free-Ranging White-Tailed Deer

Abstract Maternal investment plays a critical role in neonate survival, and adults can improve survival of offspring by defending them against predators. However, limited information exists documenting ungulate aggression toward humans in defense of neonates. During captures of neonates in spring 2007 and 2008 in north-central South Dakota, we documented 24 aggressive encounters by adult female and yearling male and female white-tailed deer (Odocoileus virginianus) defending neonates. Eleven (45.8%) aggressive encounters included yearlings accompanying adult females. Mean ages and weights of neonates that were aggressively defended were greater (P < 0.0001) than ages and weights of those that were not; adults began protecting neonates at approximately 4 days of age. Male fawns were more likely (P  =  0.013) to be defended than female fawns. Examination of our data suggests that sex- and age-biased maternal defensive behavior exists in white-tailed deer, and that deer biased maternal investment toward older, male neonates.

Influence of landscape characteristics on migration strategies of white-tailed deer

Abstract A trade-off exists for migrating animals as to whether to migrate or remain residents. Few studies have documented relationships between landscape variables and deer migration strategies. From 2000 to 2007 we captured 267 adult female white-tailed deer (Odocoileus virginianus) at 7 study sites in Minnesota and South Dakota and monitored 149 individuals through ≥3 seasonal migration periods (585 deer-migration seasons). All deer classified as obligate migrators with ≥3 migrations (range 3–9 migration seasons) maintained their obligate status for the duration of the study. Multinomial logistic odds ratios from generalized estimating equations indicated that the odds of being a resident increased by 1.4 and 1.3 per 1-unit increase in forest patch density and mean area, respectively, compared to migrating deer. Odds of being an obligate migrator increased by 0.7 and 0.8 per 1-unit decrease in forest patch density and mean area, respectively, compared to resident or conditional migrating deer. Areas inhabited by resident deer were characterized by greater number of forest patches per 100 ha and larger mean forest patch area than conditional and obligate migrant areas. Odds of migrating increased by 1.1 per 1-unit increase in deer winter severity index. Migration behavior of white-tailed deer varied among regions, and land-cover and landscape characteristics provided predictive indicators of migration strategies for deer that could have important implications for conservation, metapopulation dynamics, and species management.

Nesting Ecology of Greater Sage-Grouse Centrocercus urophasianus at the Eastern Edge of their Historic Distribution

Greater sage-grouse Centrocercus urophasianus populations in North Dakota declined approximately 67% between 1965 and 2003, and the species is listed as a Priority Level 1 Species of Special Concern by the North Dakota Game and Fish Department. The habitat and ecology of the species at the eastern edge of its historical range is largely unknown. We investigated nest site selection by greater sage-grouse and nest survival in North Dakota during 2005 – 2006. Sage-grouse selected nest sites in sagebrush Artemisia spp. with more total vegetative cover, greater sagebrush density, and greater 1-m visual obstruction from the nest than at random sites. Height of grass and shrub (sagebrush) at nest sites were shorter than at random sites, because areas where sagebrush was common were sites in low seral condition or dense clay or clay-pan soils with low productivity. Constant survival estimates of incubated nests were 33% in 2005 and 30% in 2006. Variables that described the resource selection function for nests were not those that modeled nest survival. Nest survival was positively influenced by percentage of shrub (sagebrush) cover and grass height. Daily nest survival decreased substantially when percentage of shrub cover declined below about 9% and when grass heights were less than about 16 cm. Daily nest survival rates decreased with increased daily precipitation.

Does the use of vaginal-implant transmitters affect neonate survival rate of white-tailed deer Odocoileus virginianus?

Abstract We compared survival of neonate white-tailed deer Odocoileus virginianus captured using vaginal-implant transmitters (VITs) and traditional ground searches to determine if capture method affects neonate survival. During winter 2003, 14 adult female radio-collared deer were fitted with VITs to aid in the spring capture of neonates; neonates were captured using VITs (N=14) and traditional ground searches (N=7). Of the VITs, seven (50%) resulted in the location of birth sites and the capture of 14 neonates. However, seven (50%) VITs were prematurely expelled prior to parturition. Predation accounted for seven neonate mortalities, and of these, five were neonates captured using VITs. During summer 2003, survival for neonates captured using VITs one, two, and three months post capture was 0.76 (SE=0.05; N=14), 0.64 (SE=0.07; N=11) and 0.64 (SE=0.08; N=9), respectively. Neonate survival one, two and three months post capture for neonates captured using ground searches was 0.71 (SE=0.11; N=7), 0.71 (SE=0.15; N=5) and 0.71 (SE=0.15; N=5), respectively. Although 71% of neonates that died were captured <24 hours after birth using VITs, survival did not differ between capture methods. Therefore, use of VITs to capture neonate white-tailed deer did not influence neonate survival. VITs enabled us to capture neonates in dense habitats which would have been difficult to locate using traditional ground searches.

Tonsillar Biopsy Test for Chronic Wasting Disease: Two Sampling Approaches in Mule Deer and White-tailed Deer

Preclinical antemortem testing of deer (Odocoileus spp.) for chronic wasting disease (CWD) can be important for determining prevalence rates and removing infected individuals from wild populations. Because samples with high numbers of tonsillar follicles are likely to provide earlier detection of CWD than samples with fewer follicles, the method of obtaining follicular samples may be critical when investigating disease prevalence. Between January 2003 and January 2005, white-tailed deer (O. virginianus) in southeast and southwest Minnesota and white-tailed and mule deer (O. hemionus) in Wind Cave National Park, South Dakota, were sampled using dorso-lateral and ventral-medial approaches for collecting tonsillar follicles. We obtained significantly more follicles using a dorso-lateral (median number of follicles=19) rather than a ventral-medial (median number of follicles=5.5) approach. No differences were observed in collection of tonsillar follicles that were related to sex, age class, or species of deer. We recommend the dorso-lateral approach for assessing CWD prevalence in deer populations.

Re-Evaluating Neonatal-Age Models for Ungulates: Does Model Choice Affect Survival Estimates?

New-hoof growth is regarded as the most reliable metric for predicting age of newborn ungulates, but variation in estimated age among hoof-growth equations that have been developed may affect estimates of survival in staggered-entry models. We used known-age newborns to evaluate variation in age estimates among existing hoof-growth equations and to determine the consequences of that variation on survival estimates. During 2001–2009, we captured and radiocollared 174 newborn (≤24-hrs old) ungulates: 76 white-tailed deer (Odocoileus virginianus) in Minnesota and South Dakota, 61 mule deer (O. hemionus) in California, and 37 pronghorn (Antilocapra americana) in South Dakota. Estimated age of known-age newborns differed among hoof-growth models and varied by >15 days for white-tailed deer, >20 days for mule deer, and >10 days for pronghorn. Accuracy (i.e., the proportion of neonates assigned to the correct age) in aging newborns using published equations ranged from 0.0% to 39.4% in white-tailed deer, 0.0% to 3.3% in mule deer, and was 0.0% for pronghorns. Results of survival modeling indicated that variability in estimates of age-at-capture affected short-term estimates of survival (i.e., 30 days) for white-tailed deer and mule deer, and survival estimates over a longer time frame (i.e., 120 days) for mule deer. Conversely, survival estimates for pronghorn were not affected by estimates of age. Our analyses indicate that modeling survival in daily intervals is too fine a temporal scale when age-at-capture is unknown given the potential inaccuracies among equations used to estimate age of neonates. Instead, weekly survival intervals are more appropriate because most models accurately predicted ages within 1 week of the known age. Variation among results of neonatal-age models on short- and long-term estimates of survival for known-age young emphasizes the importance of selecting an appropriate hoof-growth equation and appropriately defining intervals (i.e., weekly versus daily) for estimating survival.

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

Abstract Survival and cause-specific mortality of female white-tailed deer (Odocoileus virginianus) have been well documented in forested and agricultural landscapes, but limited information has been collected in grassland habitats typical of the Northern Great Plains. Our objectives were to document and compare survival and cause-specific mortality of adult female white-tailed deer in four distinct ecoregions. We captured and radiocollared 190 (159 adult, 31 yearling) female white-tailed deer and monitored (including deer from a previous study) a total of 246 (215 adult, 31 yearling) deer from Jan. 2000 to Dec. 2007. We documented 113 mortalities; hunting (including wounding loss) accounted for 69.9% of all mortalities and vehicle collisions accounted for an additional 15.0%. Natural causes (e.g., disease, predation) of mortality were minor compared to human-related causes (e.g., hunting, vehicle collisions). We used known fate modeling in program MARK to estimate survival rates and compare ecoregions and seasons. Model {Sseason (winter = summer)} had the lowest AICc value suggesting that survival differed only between seasons where winter and summer survival was equal and differed with fall season. Annual and seasonal (summer, fall, winter) survival rates using the top model {Sseason (summer = winter)} were 0.76 (95% ci  =  0.70–0.80), 0.97 (95% ci  =  0.96–0.98), 0.80 (95% ci  =  0.76–0.83) and 0.97 (95% ci  =  0.96–0.98), respectively. High human-related mortality was likely associated with limited permanent cover, extensive road networks and high hunter density. Deer management in four distinct ecoregions relies on hunter harvest to maintain deer populations within state management goals.