Publication Date


Date of Final Oral Examination (Defense)


Type of Culminating Activity


Degree Title

Master of Science in Biology



Major Advisor

Jennifer S. Forbey, Ph.D.


John W. Connelly, Ph.D.


James R. Belthoff, Ph.D.


Herbivores select plants and patches that generally maximize nutrient intake and minimize intake of plant secondary metabolites (PSMs). Protein is important for growth, reproduction and maintenance, but maximizing intake of protein is often limited by concentrations of PSMs that are potentially toxic to herbivores and energetically expensive to process. However, the consequences of ingesting PSM are often dose-dependent. At high doses, PSMs generally have negative physiological effects and are avoided, but some PSMs can be therapeutic against parasites at low doses and could therefore be selected. We used Greater Sage-grouse (Centrocercus urophasianus, hereafter, sage-grouse) to test how PSMs influence diet selection and parasite loads in a free-ranging avian herbivore. Specifically, we examined selective foraging by sage-grouse and how foraging patterns influence habitat use throughout winter at a mixed sagebrush site. We found that selective foraging did not influence landscape-scale habitat selection between two species of sagebrush. However, more fine-scale selection was influenced by PSMs and structural characteristics within a species. We also examined how selective foraging may influence parasite loads in sage-grouse. We tested the relationship between intake of PSMs, intestinal exposure of parasites to PSMs, and parasite loads. Parasite loads in sage-grouse were correlated with higher concentrations of PSMs, suggesting that PSMs may make sage-grouse more susceptible to parasites, or that parasites are resistant to sagebrush PSMs. This research informs basic science on foraging ecology, parasitology, and habitat use by an avian herbivore. Additionally, it provides information to managers about factors that influence diet selection and potential health consequences of ingested PSMs by wildlife.