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Parasites and disease are rarely mentioned as a serious threat to prairie grouse, probably due to their mobility and generally lower densities reducing the odds of completing parasite life cycles. Prairie chickens, being "more mobile than any other gallinaceous game" (Leopold 1931:176) might be the least susceptible to disease unless they return to a common feeding areas. Hamerstrom et al. (1957:79) pointed out, "the need for a system of well distributed winter feeding places, and gives one more reason for the superiority of food patches over hoppers and other feeding devices which concentrate birds in small spaces. Since prairie chickens are subject to several of the diseases and parasites of domestic chickens and turkeys, food patches should not be placed on ground over which domestic poultry habitually run."

Gross (1930) gives a fairly complete description of grouse parasites and diseases with a particular emphasis on another caecal worm, Heterakis gallinae. He found it in 50% of the prairie chickens he examined in Wisconsin and noted that it was probably an indication that the prairie chickens had fed on ground "polluted" by poultry droppings. Of particular concern with this parasite is that it serves as the host for the protozoan flagellate (Histomonas meleagris) which causes blackhead disease (Noble and Noble 1973). Gross (1930:36), who closely studied the heath hen, noted that, "Blackhead was an important factor in the decline of the heath hen and was probably derived from turkeys which ranged over the feeding and "drumming" fields (booming grounds) of the heath hen until blackhead made the raising of turkeys unprofitable on Martha's Vineyard Island."

Recently, disease considerations have been identified as a contributing factor in the decline of the Attwater's prairie chicken in Texas (Purvis and Silvy 1995). Disease investigations are underway with wild populations and with geese and northern bobwhite quail. Avian cholera and roundworms (Trichostrongulus tenuis) have been implicated but one of the biggest concerns is the reticuloendotheliosis virus (REV), a disease similar to AIDS which disables the immune system (Purvis and Silvy 1995). This virus was found in the Texas A & M University captive flock and in 1 wild male. Apparently this disease is common in many domestic poultry flocks (30% of all domestic chickens have it) and wild geese can carry it (Nova Silvy, personal commun.).

Diseases and parasites have not been investigated with SNG prairie grouse, nor have they been suspected as a mortality factor. One caution however could involve the expansion of confinement turkey operations along the south edge of the SNG; in particular, the disposal of dead birds and manure. If manure is disposed of in areas accessible to or favored by prairie chickens, this could be a concern. Perhaps manure should be spread at a time and place when the likelihood of prairie chicken contact is minimized or it could be worked in (tilled) soon after spreading. Herman (1963) points out the necessity of controlling diseases through manipulation of populations and habitat. When dealing with a population "on the edge", it is prudent to anticipate all the possibilities for problems in order to take protective measures.

Summary

1. Disease is generally not a limiting factor with prairie grouse, probably due to their high mobility. A notable exception is perhaps the heath hen which allegedly contacted blackhead disease from contact with domestic poultry.
   

2. Recent concern has been raised regarding the possible role of disease in the decline of Attwater's prairie chickens. It's range overlaps that of wintering waterfowl (known to carry avian cholera) and an AIDS-like disease, common in poultry, has been discovered in the Attwater's population.
   

3. The expansion of commercial turkey operation near the SNG could merit some concern as far as managing manure and dead birds to minimize contact with prairie chickens.