Year of Award
2026
Document Type
Thesis
Degree Type
Master of Science (MS)
Degree Name
Wildlife Biology
Department or School/College
W.A Franke College of Forestry and Conservation
Committee Chair
Dr. Chad Bishop
Committee Co-chair
Dr. Joshua Milspaugh
Commitee Members
Dr. Erick Greene
Keywords
Elk, Deer, Feral Horses, Abundance, Co-Occurrence
Subject Categories
Animal Experimentation and Research | Life Sciences | Other Animal Sciences
Abstract
Effective wildlife management requires understanding both population status and species interactions, particularly in systems where native and introduced species overlap. On the Yakama Nation Reservation in south-central Washington, limited information exists on the abundance, distribution, and interactions of free-roaming horses (Equus ferus caballus) with native ungulates, including elk (Cervus canadensis) and mule deer (Odocoileus hemionus). We used a network of 89 camera traps deployed across approximately 430,000 acres of forested habitat to (1) estimate species densities using the Space-to-Event (STE) modeling framework and (2) evaluate spatial and temporal co-occurrence using multi-species occupancy and site-use intensity models. Estimated densities were 0.58 elk/km² (95% CI = 0.45–0.75), 0.56 mule deer/km² (95% CI = 0.43–0.73), and 0.08 horses/km² (95% CI = 0.04–0.16), corresponding to abundances of approximately 1,013 elk, 978 deer, and 139 horses. Horse detections were concentrated in the eastern sub-basin, suggesting habitat preferences for more open, pine-dominated forests. Co occurrence analyses indicated that, after accounting for elevation, spatial overlap between horses and native ungulates was weak and not significantly different from random at broad scales. However, finer-scale temporal analyses revealed increased co-detection and site-use overlap, particularly during winter, when all three species concentrated in accessible habitats. Elk showed reduced co-occurrence with horses in winter at short temporal scales, suggesting localized avoidance, whereas mule deer exhibited greater overlap with elk. Together, these findings indicate that while wild horse densities remain relatively low and do not currently drive large-scale spatial displacement of native ungulates, seasonal conditions may intensify resource overlap and potential competition on winter ranges. This study provides the first quantitative baseline of ungulate densities and interspecific interactions on the Yakama Reservation and demonstrates the utility of camera-trap-based approaches for cost-effective, noninvasive monitoring. The results offer critical guidance for developing proactive, culturally informed management strategies addressing both population growth and multi-species dynamics on tribal lands.
Recommended Citation
Fisher, Sattie Marie, "Analyzing elk and deer interactions to identify the impact of wild horse presence on the Yakama Indian Reservation" (2026). Graduate Student Theses, Dissertations, & Professional Papers. 12738.
https://scholarworks.umt.edu/etd/12738
© Copyright 2026 Sattie Marie Fisher