404 PARASITISM AND DISEASE IN RUFFED GROUSE 



much of our knowledge of disease is gained by interpretations of the changes occurring in 

 the various tissues and aflected organs. 



The So-Called "Grouse Disease" 



In the study of birds whose fluctuations in numbers have so long been observed and specu- 

 lated upon, it is probably natural that some investigators have had preconceived notions about 

 the relation of disease to these periods of scarcity and abundance. 



The concept and term "grouse disease" came into use as early as 1838 in connection with 

 the fluctuating numbers of red grouse in Britain. Naturally, it was applied in America as 

 interest grew in the study of ruffed grouse. Naturalists, sportsmen, and other amateur observers 

 reported as "grouse disease" their discoveries of louse flies, ticks, "abdominal parasites", fowl 

 cholera and tuberculosis. A professor of bacteriology unhesitatingly remarked that the louse 

 fly was probably the carrier of the "germs" of blackhead in grouse. An ornithologist sug- 

 gested that a small stomach worm might be the cause of "grouse disease" in this country and 

 that the presence of this worm might be associated with the phenomenon known as "crazv 

 flight". 



Investigators of the British Committee of Inquiry on Grouse Disease" claimed that "grouse 

 disease" in England was mainly attributable to two types of parasitism. One involved a 

 thread-like worm, sometimes occurring in the intestine by the thousands. The other was due 

 to microscopic one-celled animals known as coccidia. These live and reproduce in the cells 

 lining the intestine. 



In this country, although about 50 parasites and a number of disease conditions have been 

 observed in ruffed grouse, none have been conclusively associated with any widespread de- 

 crease in the numbers of these birds over their entire range. 



Some parasites that are known to reach a stage of infection serious enough to cause death 

 in New York have not been found in Minnesota or even Vermont and New Hampshire. 

 Others, reported as important in Ontario, have not been encountered in New York. Patho- 

 logical conditions observed in captive grouse are observed in the wild very infrequentlv. No 

 disease recorded to date seems, therefore, to make a serious bid for the title of the "grouse 

 disease" in America or to occupy a position comparable to the parasitisms observed in Brit- 

 ish grouse. 



Factors Which May Cause Disease 



One of the convenient approaches to the study of disease is based on the natural classifica- 

 tion of the factors whose presence may excite pathological processes. Some of these may be 

 inherent in the animal itself through inherited traits and tendencies. Others originate in the 

 external environment and, under certain (dnditiniis, become iiiiinicable to the health of the 

 bird. Part of this latter group are physico-chcinical factors such as mechanical injuries, chem- 

 ical poisons and nutritional deficiencies, while part are biological, as rc|)resented by animal 

 j)arasites, plant parasites and filterable viruses. It is necessary to consider each of these in 

 some detail in order to understand their roles in liic lif<" and death of grouse. 



Mechdiiiiiil Injuries 



The conditions which residl from physical \iolciicc In llie bodies of llic birds inc known as 

 mcilKiiiical injuries or trauma. Some grouse arc struck by automobiles and trains, others fly 

 into houses or telephone wires. Shooting and predation also come in this category. 



