442 PARASITISM AND DISEASE /A' RUFFED GROUSE 



THE ROLE OF DISEASE 



It can be seen from the preceding pages that the relation of parasitism to disease and 

 disease to the life of the ruffed grouse is difficuU to evaluate. Many of the parasites do not 

 produce disease and those which do are not widely distributed throughout the range of the 

 bird. 



Though it has long been asserted as a generality that the limits of game populations are 

 probably set by disease^", clear cut examples of this are not easy to find. It seems logical to 

 assume that transmission from animal to animal takes place more readily as the population 

 increases. Furthermore, even though the increase of virulence of certain disease producing 

 organisms by rapid passage through susceptible hosts is demonstrable, the actual occurrence 

 of these phenomena in nature is not often observed. Under conditions obtaining in human 

 populations and in concentrations of domestic animals, these processes may be followed, but 

 to explain density fluctuations in wildlife on this basis, without more definite information than 

 that available to date, seems inadvisable. 



Whether disease reaches dangerous levels in natural grouse coverts is a matter for specula- 

 tion. The question is by no means solved by pointing to the absence of other factors to which 

 "die ofFs" can be attributed. The difficulties encountered in studying the role of disease in wild 

 animals foster the temptation to make broad generalizations the basis for interpreting prob- 

 lems which must be approached from a factual standpoint if sound conclusions are to be drawn. 



The possibility that local variations in abundance may occur and the fact that complete in- 

 formation on relative abundance cannot be obtained for all of the areas from which birds 

 are collected, further handicaps interpretation of autopsy findings in terms of the relation of 

 pathological conditions to the grouse population 



An additional matter for conjecture is the suggestion that, since, during periods of abund- 

 ance, transmission of disease is probably facilitated, increased hunting pressure during such 

 times would be of benefit in reducing the population to a "safe" level. As a corollarj' to this 

 is the attitude that certain of the birds shot in fall might well die of disease or other causes 

 during the winter, if they were not so harvested. 



Proper evaluation of these questions should also be based on sound observations on the 

 actual rate and mode of increase of disease during increases in abundance and on the relation 

 of the haphazard sample taken in fall hunting to the normal and diseased sectors of the bird 

 population. 



The fact that disease does occur and on occasion accounts for deaths of both wild and 

 captive grouse, necessitates its recognition as one of the factors limiting abundance. In this 

 sense, it ran no more be removed from consideration than can weather, predators and the 

 other items which in one wav or another influence the lives of grouse individuals and groups. 



Observation on pathological conditions during a period of over ten years, however, has 

 revealed no disease of epizootic proportions which would account for a sudden and wide- 

 spread disappearance of ruffed grouse. 



