250 The Ruffed Grouse 



grouse population, and the break in the increase phase, in 1938, 

 came immediately after a significant reduction in grouse numbers 

 generally in New York. While these are admittedly rough correla- 

 tions, they almost surely carry considerable significance. 



With the grouse chicks, the trend of parasite incidence is not so 

 pronounced, but rather is more consistent from year to year. Fur- 

 ther, though there is much evidence that disease is a more efifective 

 mortality factor among chicks than with adult grouse, the incidence 

 of parasitism is notably lower in the young birds. This probably re- 

 flects the fact that many of the chicks were collected when but a 

 few days old, a time when few parasites are likely to be found. The 

 nine-year record of nine hundred and thirty-two autopsies of grouse 

 chicks from 1933 to 1941 ( 1936 excluded ) shows the incidence of 

 total parasitism as follows: 1933— thirty-eight per cent; 1934— fifty- 

 eight per cent; 1935— thirty-four per cent; 1937— forty-four per cent; 

 1938— seventy-five per cent; 1939— thirty-three per cent; 1940— fifty- 

 one per cent; 1941— fifty-two per cent. The grand average was forty- 

 three per cent, compared with an average of seventy-two per cent 

 for all 2,059 adult birds examined {N. Y. S. Cons. Dept. Ann. Reps., 

 1932-42). 



DISEASE AS A LIMITING FACTOR 



Interpretation of the disease factor is among the more diJQficult of 

 all the facets of grouse ecology. It is manifestly impossible to gather 

 the vast amount of factual information that would be necessary to 

 render a well-substantiated judgment. Not only must the dead and 

 dying grouse be gathered in considerable numbers during a die-oflF 

 period, an achievement never attained by any grouse investigation, 

 but the related factors must be placed in their proper perspective 

 too. Geographical distribution of disease-caused mortality, and its 

 direction and spread are important. Correlations with grouse popu- 

 lations must be made, and hence widespread censuses must have 

 been made, another impossible task. The part played by secondary 

 hosts of the parasites, their population, condition and distribution, 

 the relation of weather (and possibly other meteorological condi- 

 tions ) to grouse health and to the disease organisms, the part played 

 by predation and hunting ( or lack of them ) , these and other matters 

 may be fundamental to an adequate understanding of grouse popu- 



