Abstract

Successful management of bighorn sheep depends on understanding the mechanisms responsible for population growth or decline, habitat selection, and utilization distribution after translocations. We studied a declining population of desert bighorn sheep in the North San Rafael Swell, Utah to determine birthdates of neonates, demographics, limiting factors, population size, probable cause of death, production, and survival. We documented 19 mortalities attributed to a variety of causes including cougar predation (n = 10, 53%), bluetongue virus (n = 2, 11%), reproductive complications (n = 2, 11%), hunter harvest (n = 1, 5%), and unknown (n = 4, 21%). Annual survival of females was 73% (95% CI = 0.55—0.86) in 2012 and 73% (95% CI = 0.55—0.86) in 2013. Adult male survival was 75% in 2012 (95% CI = 0.38—0.94) and 88% (95% CI = 0.50—0.98) in 2013. Disease testing revealed the presence of pneumonia-related pathogens. The population increased from an estimated 127 in 2012 to 139 in 2013 (λ = 1.09). Lamb:ewe ratios were 47:100 in 2012 and 31:100 in 2013. Mean birthing dates were 21 May in 2012 and 20 May in 2013. Spatial separation from domestic sheep and goats, and aggressive harvest of cougars, may have aided in the recovery of this population after disease events. Second, we investigated the timing of parturition and nursery habitat of desert bighorn sheep in the North San Rafael Swell to determine the influence of vegetation, topography, and anthropogenic features on resource selection. We monitored 38 radio-tagged ewes to establish birthing dates. We documented birthdates of 45 lambs. We used collar-generated GPS locations to perform logistic regression within a model-selection framework to differentiate between nursery and random locations (n = 750 for each) based on a suite of covariates. The top model included elevation, slope, ruggedness, aspect, vegetation type, distance to trails, and distance to roads. We used these variables to create a GIS model of nursery habitat for the North San Rafael (desert bighorns) and the Green River Corridor (Rocky Mountain bighorns). Ewes showed preference for steep, north-facing slopes, rugged terrain, lower elevation, and avoidance of roads. Our model provides managers with a map of high probability nursery areas of desert and Rocky Mountain bighorns to aid in conservation planning and mitigate potential conflicts with industry and domestic livestock. Finally, we monitored 127 reintroduced female bighorn sheep in three adjacent restored populations to investigate if the size and overlap of habitat use by augmented bighorns differed from resident bighorns. The size of seasonal ranges for residents was generally larger than augmented females. However, there was a shift in utilization distribution in all three populations after augmentation. Overlap indices between resident and augmented sheep varied by source herd. These data will help managers understand the dynamics of home range expansion and the overlap between provenance groups following augmentations.

Degree

PhD

College and Department

Life Sciences; Plant and Wildlife Sciences

Rights

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