Evaluating the Effects of Fenbendazole on Demographics of Wild Northern Bobwhite in the Rolling Plains of Texas
Request for Proposals — July 2025

Introduction

Texas has remained a stronghold for northern bobwhite (Colinus virginianus) populations across the species range; however, populations continue to decline throughout the state. Conservation partners, wildlife biologists, and avian researchers generally agree that the loss of quality habitat, habitat fragmentation, and land use changes have been the primary drivers of range wide population declines in bobwhite quail. However, recently there has been concern from the upland game bird community as to whether other factors, such as parasites, play a significant role in regional declines. As a result, these parasites, specifically eye worms (Oxyspirura petrowi) and cecal worms (Aulanocephalus pennula), have gained increased focus and conservation attention from partners.

Stressing the need for more information, studies have documented higher parasite loads and abundance in the Rolling Plains of Texas compared to other ecoregions in Texas, and researchers have documented physiological impacts to individual birds (e.g., corneal scarring, reduced fat stores). Despite this research, there is still uncertainty about the impact of parasites on quail survival and reproductive success. As a result, more research is necessary to explore whether managing parasitic infections can improve bobwhite fitness and in turn, population outcomes. One potential avenue is the use of Fenbendazole, a deworming medication that has been used in domestic livestock, poultry, captive bobwhites and other game birds, and which was recently approved for use in wild birds. Delivery methods in wild quail populations, such as medicated feed, are currently being investigated to determine practical and effective strategies for large-scale applications. However, many questions remain concerning the treatment/medication itself as an effective strategy at the individual level. Specifically, whether parasite reduction through deworming translates into measurable improvements in survival and reproductive output for wild birds.

The only way to understand the effect, if any, of eyeworm and cecal worm infections on quail survival and reproduction is through experimental studies. Experimental studies treating parasites in other avian species have been conducted. However, further research is necessary to determine the impacts a treatment has on wild northern bobwhite demographics (e.g. survival, reproduction).

Justification

Research to further our knowledge of northern bobwhites would directly address Goal 1 of TPWD's 2024 Land and Water plan. Specifically:

• Goal 1: Practice, encourage and enable science-based stewardship of natural and cultural resources.
  • TPWD will maintain the highest level of scientific validity and credibility
  • Conduct, support, and disseminate peer-reviewed research to ensure the science-based management and conservation of fish and wildlife resources.

Research Objectives

The study design should address this main objective:

1. Determine the impact of a therapeutic dose of Fenbendazole on wild northern bobwhite demographics (e.g., survival, reproduction) in the Rolling Plains of Texas.

Expected Management Implications

Individually treating bobwhites to determine survival and reproductive response is a necessary first step in understanding the effectiveness of Fenbendazole treatments as a potential management strategy. Outcomes from this research will inform biologists, landowners, and managers on using Fenbendazole to treat parasites in wild quail populations and their potential impact to desired quail populations.

Supporting Literature

• Bruno, A., A. M. Fedynich, A. Smith-Herron and D. Rollins. 2015. Pathological response of Northern bobwhites to Oxyspirura petrowi infections. Journal of Parasitology, 101(3): 364–368.
• Kubečka, B., A. Bruno and D. Rollins. 2017. Geographic survey of Oxyspirura petrowi among wild northern bobwhites in the United States. National Quail Symposium Proceedings 8:311–315.
• Hudson, P.J., D. Newborn and A. P. Dobson. 1992. Regulation and stability of free-living host-parasite system: Trichostronglus tenuis in red grouse. I. Monitoring and parasite reduction experiments. Journal of Animal Ecology 61:477–489.
• Hudson, P.J., A. P. Dobson and D. Newborn. 1998. Prevention of population cycles by parasite removal. Science 282:2256–2258.
• Olsen, A. C., L. A. Brennan and A. M. Fedynich. 2016. Helminths and the northern bobwhite population decline: A review. Wildlife Society Bulletin 40:388–393.
• Schwabe, C.W. 1950b. Studies on Oxyspirura mansoni, the tropical eyeworm of poultry. IV. Methods for control. Proceeding of the Hawaiian Entomological Society 14:175–183.
• Wyckoff, S. T., T. Judkins, N.M. Nemeth, M. G. Ruder, J. A. Martin and M. J. Yabsley. 2023. Health impacts of gastrointestinal and ocular parasites in northern bobwhite (Colinus virginianus) in western Oklahoma, USA. Veterinary Parasitology: Regional Studies and Reports 46:100936.