Horns and hotspots: detecting change in mountain sheep populations over large spatiotemporal scales

  • Author / Creator
    Karabatsos, Sofia
  • Long-term data is essential for addressing questions about how populations change over time in response to environmental variability, and natural and anthropogenic disturbance. Two species of mountain sheep (Ovis spp.) in Canada have been monitored over several decades and provided the data analyzed in this thesis. First, changes in Dall sheep horn size over 16 years in the southern Mackenzie Mountains, NWT were analyzed using a horn size trend modelling approach. We developed general linear models (GLMs) to assess horn size over time, using age at harvest and harvest year (2002 to 2017) as fixed effects, and outfitter area as a random effect. We observed no significant trend in the average horn volume of harvested rams, nor in the mean age at harvest for Dall sheep rams over this period. The current management of Dall sheep in the Mackenzie Mountains may have maintained a population of rams that do not show the decline in horn size associated with selective harvest in other jurisdictions. Second, I used 52 years of annual winter bighorn sheep surveys from the Alberta Rocky Mountains to examine changes in their distribution in the greater part of their northern winter range. Long-term census data over large geographic areas offer an opportunity to track changes in wildlife distribution over time and space, and to detect areas of interest. Using ArcGIS, two methods for analyzing spatial patterns were compared: Kernel density and hotspot analyses. Different clustered distributions and trends across time were observed for ewes and rams. Over time, ewe clusters changed from their northern historic range to new southern ranges, while ram hotspots were consistently located within their historic northern range. Ewes congregated more than rams, but all sheep congregated in larger areas during the recent period compared with earlier periods. In contrast with the hotspot approach, density analyses indicated a larger number of sheep congregations on the landscape, and no change over time. Our study provides the first macroscopic overview of bighorn sheep distribution in their largest and most intact range in the northern Rocky Mountains. These patterns of bighorn use of space over the last half a century add to our understanding of sheep resiliency to stressors and can inform the priorities for bighorn management in the future.

  • Subjects / Keywords
  • Graduation date
    Spring 2020
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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