Texas Quails: Ecology and Management

6. Diseases and Parasites of Texas Quails

89 Diseases and Parasites of Texas Quails Markus J. Peterson The rôle of disease in wild-life conservation has probably been radically underestimated. The long-prevailing under-valuation of the disease factor may be definitely associated with the limitation of the observational method of studying natural history. Leopold (1933) The mammoth work The Grouse in Health and Disease (Committee of Inquiry on Grouse Disease 1911), among other things, argued that the cecal worm Trichostrongylus tenuis (⫽ T. pergracilis) was the primary cause of “the Grouse Disease” in red grouse (Lagopus lagopus scoticus) in the British Isles. The principal impetus for this study was to determine whether infectious agents controlled variation in grouse abundance among years. This publication undoubtedly stimulated North American game-bird researchers not only to attempt similarly massive studies (e.g., Stoddard 1931; Bump et al. 1947) but also to search for their own version of “the Grouse Disease” (Gross 1925:424; Lack 1954:164), “the quail disease” (Bass 1939, 1940; Durant and Doll 1941), and the parasites of northern bobwhites (Colinus virginianus) in general (e.g., Cram 1930; Cram, Jones, and Allen 1931). Leopold (1933:325), in his influential Game Management, maintained that “density fluctuations, such as cycles and irruptions, are almost certainly due to fluctuations in the prevalence of, virulence of, or resistance to [infectious] diseases.” Thus, Leopold placed host-parasite interactions on par with other important interspecific relationships, such as predator-prey interactions. He did not, however, offer any empirical or experimental evidence to support his suppositions. About 1950, many influential wildlife scientists began to assume that infectious agents of free-roaming wildlife were ecologically unimportant , except as almost inanimate extensions of poor habitat conditions or as natural disasters (Trippensee 1948:369–84; Taylor 1956:581–83; Lack 1954:161–69). Herman (1969:325) ended his review of how diseases influence wildlife populations by stating that there was only “limited documentation that disease, as an individual factor, can drastically affect population fluctuations” and that “it is imperative that we recognize the dependency of the occurrence of disease in wildlife on habitat conditions.” Herman (1963) pointed out elsewhere, however, that few studies had been conducted in such a manner that the population-level effects of infectious agents could be documented, even if they occurred. This criticism still holds (Peterson 1996; Tompkins et al. 2002). At any rate, perceiving bacterial or viral diseases as simply extensions of poor habitat conditions or as natural disasters where management could not reasonably be brought to bear—much like hurricanes or volcanic eruptions —led North American wildlife ecologists and managers to neglect these important interspecific relationships (Peterson 1991a). Conversely, since the early part of the twentieth century, those interested in parasite systematics continued to study their favorite taxa in wild hosts, including northern bobwhites and other quails. Such 6 90 Ecology and Life History of Texas Quails efforts tended to emphasize host lists, parasite descriptions, and revisions of taxonomic relationships. Similarly, those interested in the diseases of pen-reared bobwhites continued to publish case reports and study diseases important to these poultry operations. These articles, however, often were cataloged under key words related to particular, often now obsolete, parasite taxonomic names rather than terms transparent to wildlife scientists (e.g., “disease” or “parasite”). This renders comprehensive literature searches difficult for many interested in the infectious agents of quails. Host-Parasite Ecology Although others previously addressed host-parasite interactions from an ecological perspective, Anderson and May (1978) and May and Anderson (1978) provided the basic theoretical framework still used for evaluating host-parasite interactions ecologically. They demonstrated how parasites could, under certain circumstances, not only cause disease in individual animals but also regulate host populations. Probably in part because of May’s stature as a leading theoretical ecologist of this period, studying host-parasite ecology in wild populations suddenly was again orthodox, and numerous theoretical and a few applied publications grounded in these ideas soon followed. These included the wellknown studies demonstrating that T. tenuis could regulate red grouse populations under certain circumstances (e.g., Hudson 1986; Dobson and Hudson 1992; Hudson, Dobson, and Newborn 1992, 1998; Hudson, Newborn, and Dobson 1992). This renewed interest in the relationship between parasites and wild hosts eventually spread to North America, although few studies based on this theoretical foundation specifically addressed the infectious agents of northern bobwhites, let alone other quails occurring in Texas. Ecologically, parasites are organisms that meet the following three conditions: utilizing their hosts as habitat, depending nutritionally on the hosts, and...