With the recent outbreaks of avian influenza in waterfowl across the United States as well as heightened attention and concern regarding bobwhite parasites, discussions of disease have been a common topic among hunting parties this season. The following is a brief summary of interpreting disease findings, common diseases of bobwhite, and what a manager can do to mitigate their risks.
What is a disease?
A commonly adopted definition by wildlife biologists is “any impairment that interferes with normal functions, including responses to environmental factors such as nutrition, toxicants, and climate; infectious agents; inherent or congenital defects; or a combination of these factors” (Wobeser 2013). With such a broad definition, it’s easy to understand how several things can cause disease in bobwhite. However, the mere presence of these disease-causing factors are not always a concern. As a matter of fact, bobwhite often host several disease agents (e.g., bacteria, worms, protozoa) or are exposed to many factors that could cause disease yet never do. Conversely, some disease agents have great potential to cause death, illness, or impairment. We often refer to a disease agent’s degree of harm as virulence. For example, the avian influenza (AI) outbreak recently documented in the US was caused by a virulent strain of the AI virus, swiftly causing mortality in ducks.
Interpreting Disease Studies
Surveys are incredibly important for monitoring disease risks. However, general disease screening surveys are limited by survivorship bias. Survivorship bias occurs when researchers survey groups of wildlife that have already gone through a process of selection (i.e., the survivors). In other words, the documentation of a disease agent could mean that it could pose a risk in the future, or alternatively, it could mean that a bird can host the agent without resulting in disease (caveat: under the conditions it was sampled). Because of this uncertainty, it is important to have knowledge of a disease agent’s virulence when interpreting survey data as well as the conditions of when and where surveys are conducted (e.g., season, animal density, location, etc.).
What diseases might concern a quail manager?
Top-of-mind currently are avian influenza (AI), aflatoxicosis, coccidiosis, and helminthiasis (i.e., parasitic worm infections). Others are also often scrutinized including pullorum typhoid (Salmonella), avian pox, West Nile Virus (WNV), quail enteritis, quail bronchitis, trichomoniasis, histomoniasis (aka blackhead), and several more.
While some of these diseases can be quite virulent, they are rarely considered limiting factors to wild bobwhite populations. Certain conditions can, however, increase risks of disease outbreaks. Fortunately, most of these conditions are absent in wild quail populations. For example, several of these pathogens are transmitted directly from one bird to the next, often through fecal-oral routes. Crowding, stress, and poor cleanliness often leads to pen-raised quail defecating and eating in the same area. As a result, outbreaks of coccidiosis are relatively common in commercial settings but rare in wild quail populations despite the pathogen (Eimeria protozoa) sometimes being present. Diseases caused by viruses like AI, WNV, pox, and quail bronchitis are also all directly transmitted and more common in pen settings than in the wild. The effects of helminthiasis in quail are less known. Several species of parasitic worms infect wild bobwhite and healthy birds can often host dozens to hundreds of worms (of various species). Some of these worms are directly transmitted and some require intermediate hosts (i.e., the worm has to develop in another animal, typically an arthropod). The virulence of most worms found in quail are poorly documented and experimental studies are needed to determine the virulence to bobwhite and whether the various species of worms are of management concern. Lastly, aflatoxicosis is caused by a mycotoxin resulting from the fungus, Aspergillus that grows on grain under certain environmental conditions. Conditions that promote growth of this fungus therefore increase the risk of aflatoxins to animals that consume grain.
Managing to mitigate disease risks
So, what can a manager do? Given the modes of transmission and risk associated with different diseases, flock types (wild vs. pen-reared), and scenarios, we’ve developed a handful of broad considerations for managers:
- Pre-release programs should be isolated to their own hunt courses, and ideally, far away from wild quail courses (i.e. not mixed).
- Birds for pre-releases should be secured from reputable breeders who test their flocks.
- Milo is a safer choice of grain for supplemental feeding compared to corn for reducing the risk of aflatoxins.
- Storing grain in clean, dry conditions is important.
- Purchase grain from reputable dealers who adequately store their grain and-or test it.
- Broadcast feeding rather than stationary feeders or piling of grains is best for reducing conditions that support the fungus (Aspergillus) that ultimately leads to aflatoxicosis. Spreading grain may also reduce infectious disease transmission between quail by not concentrating them together.
- Maintain high quality habitat through management, including prescribed fire. Fire is known to interrupt life cycles of various ectoparasites like ticks and the pathogens they carry. Less is known about fire’s effects on life cycles of indirect life-cycle parasites like the notorious eyeworm and cecal worms which persist in intermediate hosts (arthropods). Habitat management at large scales to support large populations is also a hedge for population resilience if a virulent disease outbreak were to ever occur.