Game Management

XIII. CONTROL OF DISEASE

CHAPTER XIII CONTROL OF DISEASE This chapter is not a compendium of available knowledge on game diseases. Larger volumes than this have been written about a single disease of a single species. It aims rather to sketch, in bold outlines, the probable role of the disease factor in game productivity, and the possibilities of its control in game management. The principal purpose is to help the game manager or thinking sportsman orient his mental picture of the mechanisms, scope, and power of wild-animal diseases in the light of what is now known about them, so that his field observations can be pertinent and his co-operation with specialists more intelligent. New knowledge is piling up rapidly. If the reader has biological training, he may have to unlearn certain principles which were taught him a few years ago as accepted truth. By the same token, this sketch may not long remain up-to-date. It is a pity that the narratives of scientific exploration in this field-as fantastic a romance as any Arabian Nights-should either be masked by such technical verbiage as to mean nothing to the thinking layman, or translated for the popular press in such kindergarten terms as to be no longer true. These explorations have divulged a fabric of relationships in the biotic community of great import not alone to conservation, but to sociology and philosophy as well. Take, for instance, the growing realization that disease organisms , despite their ruthless decimation of individuals, tend constantly to evolve toward a symbiotic relationship-i. e., a relation of mutual tolerance-to their host species. We have already seen a hint of something parallel in predators, and the tendency of the game itself to remain in or return to some sort of equilibrium with the capacity of its environment seems to be merely another expression of the same thing. It is not for this book to suggest social interpretations of these phenomena, but the game manager, if he is so disposed, 3Z4 CONTROL OF DISEASE may well regard his field as an outdoor laboratory for the study of Homo sapiens. Importance of Disease. The role of disease in wild-life conservation has probably been radically underestimated. Disease, for instance, is not commonly thought of as controlling predators as well as game, yet the drift of the recent evidence is strongly in this direction, especially mammalian predators. That disease is the outstanding control of buffer foods for predators, such as rodents, is now in many instances an established fact. There are grounds for suspecting that disease may in some case~ be the factor which delimits the geographic range of game specIes. Density limits of game populations are in many species probably set by disease. This has long been asserted as a generalization , but recent years have begun to show specific cases. Density fluctuations, such as cycles and irruptions, are almost certainly fluctuations in the prevalence of, virulence of, or resistance to diseases. Some diseases also disturb the sex ratio, and may affect fertility. This long-prevailing under-valuation of the disease factor may be definitely associated with the limitations of the observational method in studying natural history. It is difficult or impossible to "observe" disease, because of the promptness with which diseased wild animals disappear or succumb to natural enemies. In most species it is only during epizootics, when the sick or dead become so numerous as to satiate all the predators, that they are seen at all. Hence disease did not yield to the observational method of study. Understanding began only when field observations were combined with the experimental or laboratory technique of modern science. Feasibility of Control. Most laymen and many scientists entertain mental reservations as to the practical utility of wildanimal disease studies. "You cannot doctor sick birds." With this terse and (to his mind) conclusive rejoinder the layman often attempts to relegate the whole subject to the category of interesting but useless knowledge. He, of course, overlooks the obvious fact that" doctoring" is of recessive importance in health control, even in domesticated GAME MANAGEMENT species and human beings. He overlooks also that the real determinants of disease mortality are the environment and the population, both of which are being" doctored" daily, for better or for worse, by gun and axe, and by fire and plow. Pessimistic attitudes toward disease control are further accentuated by the extreme complexity of many of the disease mechanisms...