Managing Parasitic Infection in Wild Northern Bobwhite (Colinus virginianus): Further insights into Helminth Epidemiology and the Pharmacological Efficacy of an Anthelmintic Feed

Northern bobwhite (Colinus virginianus) are a culturally, ecologically, and economically valuable upland game bird whose populations have experienced decades-long declines across much of their historical range. While habitat loss, fragmentation, and climate extremes are well-established drivers of this trend, bobwhite populations have continued to decline even in regions with intensive habitat management and favorable weather conditions. This pattern suggested the presence of additional, undiscovered stressors. Emerging research has identified parasitic helminths, specifically the eyeworm Oxyspirura petrowi and the cecal worm Aulonocephalus pennula, as contributors to population suppression in wild bobwhite, particularly in the southern Great Plains. These parasites often infect >90% of sampled birds, with individuals harboring mean intensities of several dozen to several hundred worms during epidemic periods. Despite widespread infection and evidence of associated pathology, no practical field-level interventions previously existed to control helminth burdens in wild bobwhite. The goal of this dissertation was to provide further insight into the epidemiology of helminth infections in bobwhite and to assess the pharmacological effectiveness and long-term field performance of a medicated anthelmintic feed, QuailGuard®, that uses fenbendazole as the active ingredient. Research was conducted in western Oklahoma and West Texas as well as at the Wildlife Toxicology Laboratory, employing a combination of field trials, laboratory studies, and pharmacokinetic modeling to attain research goals. First, I investigated the epidemiology of O. petrowi and A. pennula. I validated a method for recovering O. petrowi eggs from soil and found that potentially infectious ova could persist across both summer and winter seasons, supporting the possibility of year-round transmission. Insect intermediate host data revealed significantly reduced parasite prevalence on properties that had been treated for several years, suggesting that host-directed treatments have landscape-scale impacts. I also documented rapid reinfection of wild bobwhite within 3–4 months of treatment. The rapid reinfection was likely due to a robust environmental reservoir of infectious parasites in the forms of infections eggs and infected intermediate hosts. Next, I evaluated feed consumption thresholds and drug absorption in individual bobwhite. Controlled in vivo studies demonstrated that consuming ≥38.9g of medicated feed over a 21-day period resulted in complete clearance of O. petrowi. Pharmacokinetic profiles of fenbendazole and its bioactive metabolite, oxfendazole, confirmed effective drug uptake and rapid metabolism, resulting in a low risk of bioaccumulation and secondary exposure to predators. Field trials conducted on two sites over multiple years demonstrated QuailGuard® remained highly effective even 4-6 years after the initial treatment. Collectively, these findings support the conclusion that targeted anthelmintic treatment using medicated feed is an effective, scalable, and practical conservation tool. While habitat restoration and management remain critical long-term goals, integrating parasite management into existing conservation strategies may enhance the resilience of bobwhite populations, particularly on private lands where traditional habitat interventions are limited by cost, scale, and feasibility. Future work should refine treatment protocols based on ecological context and parasite epidemiology, but these results mark a significant advancement in evidence-based, field-applicable parasite control for wildlife conservation.