The Diseases and Parasites of Wild Ruffed Grouse 251 



lation changes. So it is no wonder that we cannot yet paint a very 

 clear picture of the significance of disease among grouse. 



Despite all of the defects in our knowledge, certain conclusions 

 can be made with fair accuracy and other probabilities can be 

 suggested. 



During most years, disease is not a primary mortality agency of 

 grouse in any given area. A considerable incidence of most of the 

 parasitic organisms that aJBFect grouse may be considered normal and 

 not a serious threat. 



The incidence of disease organisms and the intensity of the indi- 

 vidual infections and infestations are directly related to the popula- 

 tion density of the grouse. When grouse are scarce, they will have 

 little disease; as the numbers of grouse increase, parasitism and 

 disease will increase, and when grouse are abundant, disease will 

 generally become more virulent and an important cause of mortality 

 in local areas. 



When grouse are abundant over a wide range, losses from disease 

 will probably occur from a combination of several species of para- 

 sites; and when epizootics do occur from a single species of parasitic 

 organism, the eflFects are likely to be very local and unevenly dis- 

 tributed. 



It is probable that there is a significant relationship between 

 disease mortality in grouse and weather conditions. It is well-known 

 that some parasites reproduce more abundantly under certain me- 

 teorological conditions than under others, as for example in wet 

 weather as contrasted to dry. Boughton ( 1937 ) discussed this matter 

 at some length. He concluded, "... a definite correlation between 

 the degree of parasitism and the meteorological and topographical 

 factors appears to occur." 



When disease becomes an important mortality factor of grouse, 

 it probably is primarily effective in killing the young birds during 

 the summer. 



When serious declines in grouse populations occur over consider- 

 able areas, declines of the type that have been called cyclic, disease 

 almost certainly plays a part, and just as certainly shares the re- 

 sponsibility for causing the losses with other major factors as weather 

 conditions and predation. 



