Feral Horse Movement, Habitat Selection, and Effects on Pronghorn and Greater Sage-grouse Habitat in Cold-arid-steppe

ISBN-10
ISBN-13
9798515255886
Category
Elk
Pages
154
Language
English
Published
2021
Author
Jacob D. Hennig

Description

Increasing populations of feral horses (Equus ferus caballus) on western North American rangelands threaten the provisioning of ecosystem services and the stipulation for public lands to be managed for multiple uses. Feral horse grazing can decrease vegetation cover and effect species composition, alter soil structure, and negatively influence faunal communities. Partisan viewpoints regarding the role of feral equids on public rangelands underscore the need for management strategies based on sound science, but information on basic feral horse ecology is limited. Increased understanding of vegetation and soil responses to varying levels of horse use and site-specific information on movement patterns and habitat use are necessary to implement successful management plans. Thus the aim of my dissertation was to increase understanding of feral horse ecology in arid shrublands of western North America and to evaluate the potential for horses to influence habitat quality for co-occurring wildlife species. I present a broad introduction to my research in Chapter 1, with the following four chapters formatted for journal-specific requirements. In Chapter 2, I conduct a systematic review to record all telemetry-collared wild and feral equids worldwide and evaluate the relative risk of collar-related complications for equids compared to commonly collared North American ungulates, elk (Cervus canadensis), mule deer (Odocoileus hemionus), and pronghorn (Antilocapra americana). We found 1,089 collared equids prior to 2017 but while mortality rates for equids were lower than for elk, mule deer, and pronghorn, the lack of sufficient information prevented a critical assessment of relative collar-related complications. Consequently, we encourage explicit reporting of collar-related issues, or lack-thereof, in published literature. This chapter was published in Wildlife Research in 2020 with co-authors J. Scasta, J. Beck, K. Schoenecker, and S. King (Hennig et al. 2020. Systematic review of equids and telemetry collars: implications for deployment and reporting. Wildlife Research 47, 361-371). Chapter 3 examined the variation in greater sage-grouse (Centrocercus urophasianus) habitat quality metrics along a gradient of feral horse use. We found intensity of feral horse use to be an informative predictor of mean grass height and the proportion of bare ground, but other habitat metrics were better explained by topographic and temporal variation. Bare ground linearly increased with increased feral horse use and grass height declined after approximately 638 horse fecal piles/ha. Our results suggest that reductions in feral horse population sizes may limit soil erosion and maintain desired herbaceous structure, but additional management actions are likely needed to sustain high-quality greater sage-grouse habitat. This chapter is in revision at Journal of Arid Environments with co-authors J. Beck, C. Duchardt, and J. Scasta. The objective of Chapter 4 was to understand how differences in digestive morphology and feeding strategy influence the movement syndromes of sympatric ungulates. We found that cecal digesting and bulk roughage feeding feral horses exhibited a more sedentary movement syndrome than ruminating and concentrate selecting pronghorn. Reliance on predictable locations of free-standing water and patches of high vegetation biomass were strong drivers of the more sedentary movements of horses corresponding to their cecal digestion strategy.. Pronghorn unexpectedly showed little selection for relatively unpredictable patches in vegetation green-up, with the lack of need for free-standing water the most likely driver of their relatively nomadic movement. This chapter has been formatted for submission to Journal of Animal Ecology with co-authors J. Scasta and J. Beck. Chapter 5 provides a comparison of seasonal resource selection between co-occurring populations of feral horses, greater sage-grouse, and pronghorn and predicts the proportion of occurrence overlap between the species. Pronghorn have a high proportion of occurrence overlap with horses in both summer (0.84) and winter (0.90), while greater sage-grouse have the highest amount of overlap in the summer season (0.91). Our results suggest that pronghorn face potential competition and habitat alteration from horses year-round, whereas the threat of decreased habitat quality is most prevalent for sage-grouse during later brood-rearing. This chapter has been formatted for submission to Journal of Wildlife Management with coauthors J. Scasta, A. Pratt, C. Powell, and J. Beck.

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