The Diseases and Parasites of Wild Ruffed Grouse 225 



bird population declined that winter more than usual, but recov- 

 ered quickly the next year, and there was no conclusive evidence of 

 disease being a major decimating agency. And so it has been each 

 succeeding year since in New York. 



During the 1930's the results of three other investigations on the 

 grouse disease factor were reported. Working in Ontario, Canada, 

 Clarke (1936) concluded that a protozoan blood parasite, Leuco- 

 cytozoon bonasae ". . . is most probably the organism responsible 

 for the dying-off of grouse." Boughton ( 1937 ) reported on examina- 

 tions of five hundred and sixty grouse, mainly from Minnesota, and 

 was unable to draw definite conclusions as to the part played by 

 disease in causing grouse mortality. He did feel that ". . . none of 

 the parasites found during the present survey (which does not in- 

 clude examinations of adult grouse during the months of June, July 

 and August ) have been directly responsible for the mortality among 

 the adult ruffed grouse during the year 1933-34, when a decrease 

 in the grouse population was reported." However, he added that 

 "the possibility still exists that parasitism is the cause of 'epidemics' 

 in adult grouse during the summer months ... It appears more 

 probable . . . , however, that any mortality that did take place 

 might have occurred in the young grouse . . ." More than three hun- 

 dred grouse were autopsied in connection with the Michigan grouse 

 study by Fisher ( 1939 ) . He concluded ". . . that parasites and dis- 

 eases of the ruffed grouse appear to be a major factor in the decima- 

 tion of these birds in Michigan. It is evident that in order to account, 

 if possible, for the periodic fluctuation in the population of the ruffed 

 grouse in Michigan, it will be necessary to continue laboratory 

 studies and field observations on these parasites that infest the 

 species." 



It seems apparent that the several investigators each feel that there 

 is something vital in the grouse's disease relationships but they are 

 not quite sure what it is or how it works. Before considering further 

 the epidemiology of these diseases, let us review those that are the 

 more prevalent. 



CHARACTERISTICS AND OCCURRENCE OF DISEASE AGENTS 



The diseases and parasitic conditions in the ruffed grouse, and 

 their causative agents, may conveniently be grouped in the follow- 

 ing categories: 



