Reassessing Survival, Movement, Resource Selection, and SIghtability of Pronghorn in Western South Dakota

Limited information exists on the survival, movements, resource selection, and densities of pronghorn (Antilocapra americana) inhabiting sagebrush-steppe regions within the Dakotas. Primary objectives of this study were to develop a sightability model for aerial surveying and to document survival rates and movement patterns for pronghorn in western South Dakota. Secondary objectives were to estimate seasonal home ranges, daily movements, determine cause-specific mortality, and evaluate summer and winter resource use and selection. Additionally, we evaluated exposure of pronghorn to novel diseases including Epizootic Hemorrhagic Disease (EHD), West Nile Virus (WNV), Blue Tongue Virus (BTV), Bovine Viral Diarrhea Virus (BVDV), Neospora, and Parainfluenze-3 (PI-3). From February 2015 to December 2016, we monitored 69 adult, 34 yearling, and 92 fawn pronghorn within and surrounding Butte County, South Dakota. Overall survival rates for adults and yearlings were 0.87 (95% CI, 0.79 – 0.93) and 0.78 (95% CI, 0.59 – 0.90), respectively. Mean survival rate for fawns pooled across years was 0.66 (95% CI, 0.56 – 0.75) with predation (n = 15) as the leading cause of mortality. In comparison, predation accounted for 2 adult and 5 yearling mortalities overall. In 2015, we collected blood samples and extracted serum from 50 (40 adult, 10 yearling) pronghorn. Disease exposure was variable and ranged from 5% for BTV and BVDV to 67.5% for WNV; EHD (60%), PI-3 (40%), and Neospora (10%) were intermediate relative to exposure. We calculated 124 home ranges and documented 19 seasonal movements from 67 adult female pronghorn using 5,297 locations. Likewise, 30 home ranges and 17 seasonal movements were documented from 33 yearling pronghorn using 1,578 locations. We classified 4 individuals as conditional migrators and the majority of adult females (≥86.1%) as non-migratory. Over the course of 4 seasonal periods (i.e., spring 2015, fall 2015, spring 2016, fall 2016), mean distance traveled for dispersing adult female pronghorn between summer and winter areas ranged from 11.9 km (SE = 1.3) to 14.8 km (SE = 3.8). Twelve of 40 fawns captured in spring 2015 were monitored through their second summer as yearlings. We classified 7 of 12 individuals (58%) as dispersers from natal home ranges. Mean distance traveled for dispersing yearlings over 3 seasonal periods ranged from 12.9 km (SE = 1.4) to 15.4 km (SE = 2.0). Mean 95% winter and summer home ranges for adults were 73.7 km² and 30.3 km², respectively. In comparison, yearling 95% winter and summer home ranges were 75.9 km² and 53.7 km², respectively. Daily distance traveled by adult female pronghorn differed (P \u3c 0.00001) between summer (May-October) and winter (November-April). However, we observed higher daily distances traveled by yearling pronghorn during April – June when some individuals wander during establishment of permanent home ranges. Highways seemed to be a significant barrier in impeding pronghorn movement across our study area with 42% of study individuals within 1 km of a highway and only 4 documented crossing occasions. We used Design III analyses to evaluate resource selection from 4,786 visual observations collected via radio-telemetry. Our study area was classified as native rangeland, alfalfa/hay, winter wheat/small grains, and harvested/idle encompassing minimum convex polygons for 35, 40, and 49 adult female pronghorn during summer 2015, winter 2015-16, and summer 2016 seasons, respectively. Adult female pronghorn did not use habitat in proportion to its availability during all seasons examined (P \u3c 0.001). Analyses demonstrated that in 2015 and 2016 pronghorn selected for alfalfa/hay (2015: ŵ = 3.688, CI = 1.450 – 5.925; 2016: ŵ = 1.417, CI = 1.178 – 1.655) and harvested/idle fields (2015: ŵ = 6.000, CI = 6.000 – 6.000; 2015: ŵ = 6.375, CI = 6.375 – 6.375) during summers. During winter 2015-16, pronghorn selected for winter wheat fields (ŵ = 6.077, CI = 4.793 – 7.361). Selection of alfalfa/hay and winter wheats fields was evident in pronghorn groups found in the southern regions of our study area. Furthermore, we observed pronghorn selecting positively for water source