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Evaluation of Aerial Transect Surveys, Survival, and Movements of Pronghorns in Western South Dakota
Dissertation - University Access Only
Doctor of Philosophy (PhD)
Department / School
Wildlife and Fisheries Science
Jonathan A. Jenks
We evaluated aerial transect surveys, survival, and movement of pronghorns (Antilocapra americana) from 2002-2005 in western South Dakota. Survival and cause-specific mortality of pronghorns (Antilocapra americana) have been well documented in several western states and Canadian provinces; however, no information has been collected in western South Dakota where mixed-grass prairie habitats characterize rangelands. We documented human-related mortality (e.g., hunting, illegal harvest, vehicle collision) as the greatest cause of adult pronghorn mortality (34%), of which 26% (n = 9) of adult deaths were attributed to firearms hunters. Annual survival rates pooled across years of adult radiocollared pronghorns were 0.87 (n = 138, SE = 0.05) and 0.86 (n = 73, SE = 0.07) for Harding County and Fall River counties, respectively. Twelve week post-capture (summer) survival rates for neonates pooled over years were 0.92 (n = 52, SE = 0.07) and 0.62 (n = 57, SE = 0.13), for Harding and Fall River counties, respectively. We documented coyote (Canis latrans) predation as the primary cause of mortality for neonates in western South Dakota and that microhabitat characteristics at neonate bed sites differed between northwestern (Harding County) and southwestern (Fall River County) South Dakota. More intensive aerial predator control may increase neonate survival in Fall River County. Management of rangelands throughout western South Dakota that maximizes overstory (grass, shrubs) height, understory height, and distribution of clumped, vertical structure would provide neonates with adequate concealment cover (NCC) for protection from predators, thereby increasing 4 and 12 week post-capture survival. Of 57 pronghorn fawns captured and fitted with mortality sensing radiocollars during May 2002-2003, 23 were killed by predators during their first two months of life. The remaining 34 individuals (20 in Harding County, 14 in Fall River County) were radio-tracked through 15 months of age, by which time all individuals had established permanent home ranges. We classified 56% (n = 19) of fawns as dispersers and 44% (n = 15) as residents. Eighty-four percent (n = 16) of dispersers departed natal home ranges in late October and occupied winter home ranges for 102 to 209 days before dispersing to permanent home ranges during April 2003 and 2004. Dispersal distances from natal ranges to permanent home ranges varied from 6.2 to 267.0 km. Winter home range sizes for all individual pronghorns varied from 39.4 to 509.6 km2. Permanent home range size for all individuals varied from 15.5 to 166.1 km2. Mean 95% permanent home range size differed (P = 0.06) between residents (mean = 97.3 ± 15.1 km2) and dispersers (mean = 48.6 ± 16.0 km2) but were similar (P = 0.97) among sexes. Mean dispersal distance from natal to permanent home ranges was similar (P = 0.35) for males (mean = 54.2 ± 21.0 km) and females (mean = 26.3 ± 19.9 km). We suggest that dispersal was stimulated, in part, by habitat quality (i.e., patchiness) and pronghorn density. We hypothesize that as habitat patch size decreases, home range sizes and distance traveled during pre-dispersal and dispersal movements by pronghorns increase. From January 2002 to August 2005, we monitored movements of 78 adult (≥ 1.5 years) female pronghorns in western South Dakota. We collected 8,750 visual locations, calculated 204 home ranges, and documented 19 seasonal movements. Eighty-four percent (n = 53) of pronghorns were non-migratory and 10% (n = 6) were conditional migrators. Mean distance between summer and winter range was 23.1 km (SE = 2.8, n = 13). Four pronghorns (6%) dispersed a mean distance of 37.6 km (SE = 12.4) with 1 female moving a straight-line distance of 75.0 km. Winter and summer home range use areas varied (P < 0.0001) between study sites. Mean 95% winter and summer home ranges of pronghorns were 55.5 km2 and 19.7 km2 in Harding County and 127.2 km2 and 65.9 km2 in Fall River County. Mean daily distance traveled during winter and summer by pronghorns differed (P ≤ 0.013) between study sites. Mean daily distance traveled during summer and winter in Harding and Fall River counties was 1.8 and 2.6 km, and 2.9 and 3.1 km, respectively. Maximum daily distances traveled by pronghorns in Harding and Fall River counties were 22.2 and 31.9 km, respectively. We suggest that regional differences in seasonal home ranges and distances traveled by migratory pronghorns between Harding and Fall River counties were associated, in part, with differences in summer and winter range composition between these regions. Non-migratory behavior exhibited by pronghorns in western South Dakota was associated with favorable climatic conditions during winter 2002-2004. We provide data beneficial to biologists managing northern populations of pronghorns within an eastern extension of sagebrush steppe communities by describing relationships between favorable climatic conditions, seasonal home ranges, and pronghorn movements. During years with milder winters, we recommend the continued use of spring aerial surveys to obtain data on pronghorn demographic parameters. We also recommend that South Dakota game managers consider how timing of winter arrival and winter weather severity could influence seasonal movements by pronghorns across game management unit boundaries, thereby influencing hunter harvest and overall statewide management objectives for the species. Aerial total counts and line transect (LT) sampling have been used by game managers to estimate abundance of a wide variety of ungulate species throughout western North America. For the last 6 decades the South Dakota Department of Game, Fish and Parks has used aerial total counts to monitor dynamics of pronghorn populations within game management units. However, evaluation of aerial survey methodology for visibility biases has not been previously conducted in western South Dakota. During spring 2004, we evaluated total count surveys for visibility biases using 60 radiocollared adult female pronghorns throughout Harding (n = 35) and Fall River (n = 25) counties. We observed 115 of 200 (57.5%) pronghorn groups and failed to observe 85 of 200 (42.5%) groups containing radiocollared individuals. Group behavior, topography, group size, and cover type were important factors influencing pronghorn sightability throughout western South Dakota. Our results indicated that as landscape complexity increased, the number of factors that influenced sightability of pronghorns also increased. Line transect sampling was conducted in 2 pronghorn game management units in Harding County during May 2004. Total count population estimates were 35-68% of LT population estimates. Given the precision of our data, we found that LT sampling provided reasonable estimates of density and population size in our survey areas. However, 95% confidence intervals for Harding County pronghorn population estimates (N = 14,535, 95% CI = 11,564 - 18,268) were large but comparable to previous studies. We recommend future LT sampling be conducted prior to or immediately following parturition and that Harding County be stratified into north and south units rather than east and west units to minimize observer fatigue and variation in the number of pronghorn groups observed on each transect. Use of two experienced observers during all LT sampling also would reduce confidence intervals and increase precision of pronghorn density and population estimates. South Dakota game managers should integrate LT sampling into high-density pronghorn populations and validate and augment total count estimates for low-density populations using LT surveys. South Dakota game managers also should consider validating pronghorn sightability models during future aerial surveys in game management units that differ markedly in habitat complexity and density of pronghorn from areas used in this study.
Library of Congress Subject Headings
Pronghorn -- Monitoring -- South Dakota
Pronghorn -- Mortality -- South Dakota
Pronghorn -- Seasonal distribution -- South Dakota
Aerial surveys in wildlife management
Includes bibliographical references
Number of Pages
South Dakota State University
Copyright © 2006 Christopher N. Jacques. All rights reserved.
Jacques, Christopher N., "Evaluation of Aerial Transect Surveys, Survival, and Movements of Pronghorns in Western South Dakota" (2006). Electronic Theses and Dissertations. 481.