• Effects of Human Activity on the Distribution of Desert Bighorn Sheep Along the Border in Southwestern Arizona and Northern Sonora

      Christianson, David; Antaya, Andrew Martyn; Koprowski, John; Coleman, Tyler (The University of Arizona., 2018)
      Changes in species distribution in areas with human activity may be the result of either spatial-temporal avoidance of those areas, or as the result of a decrease in survival and recruitment within those areas. My research examined the effects of human activity on the distribution of desert bighorn sheep (Ovis canadensis mexicana) along the border in southwestern Arizona, USA and northern Sonora, Mexico. I surveyed 33 transects (256 sites) on foot from February 2017 to January 2018, with 8 of 33 transects re-surveyed during this period. Human use at each site was indexed by trash category (0 pieces of trash, 1-10 pieces of trash, >10 pieces of trash). Bighorn sheep fecal pellets were used as detections of bighorn sheep. This study used a novel approach to survey replication. Old, white fecal pellets and newer, brown fecal pellets were used as the first and second temporal replicates of a survey, respectively. I used a hierarchical occupancy model to estimate probability of detection and occupancy, with human activity and environmental covariates as explanatory variables. Human activity as indexed by trash had a non-statistically significant but potentially biologically significant negative effect on occupancy. Elevational site position on mountain was positively related to occupancy in Mexico, but not in the USA. Height of the mountain above adjacent valley bottom was positively related to occupancy in the USA, but not in Mexico. These results suggest that bighorn sheep use habitat differently in the USA than in Mexico, likely due to the differences in human activity within each country. Small mountains should be recognized as habitat for desert bighorn sheep, even though in some areas, those features may be infrequently selected by sheep. Conservation efforts should recognize that 'atypical' bighorn sheep habitat may hold value for restoring or maintaining bighorn sheep populations.