PARASITES OF WILD GROUSE 429 



1. Coccidia infecting one species of host seldom infect another. E. dispersa is an exception 

 to this principle since it has been reported from a number of birds. 



2. Oocysts under suitable conditions may survive for a year or more on the ground. 



3. In all likelihood, adult birds previously infected may serve as carriers of infection for 

 susceptible birds. 



4. In some types of infection, there is an age resistance exhibited by the host. 



5. The severity of infection is determined, among other things, by the number and species 

 of the infective stages eaten. 



6. Recovery from infection results in a state of immunity in the host. The extent and 

 nature of this immunity and the promptness with which it is brought about depends 

 upon the species of coccidia and the severity of the initial infection. 



There is no reason to doubt that these factors operate in the spread of coccidiosis in ruffed 

 grouse. Obviously, until detailed laboratory experimentation and further field observ atiuiis are 

 done with coccidia of grouse, one may only conjecture on the exact operation of these factors. 



Pathogenicity. No instance of severe coccidial infection has been encountered by the 

 Investigation. For the most part, the presence of coccidia has been detected by the examina- 

 tion of smears from tlie intestinal mucosa. No attempt has been made to identify the species 

 of oocysts encountered. It is interesting to record that on one occasion during the early 

 attempts to propagate grouse in confinement, fecal examinations* carried out as a part of the 

 routine examination, revealed large numbers of oocysts in the feces. Despite this, the half- 

 grown birds showed no symptoms of disease nor was there any clinical evidence that intestinal 

 inflammation was present. 



Incidence and Importance. As is evident from table 64 and table 67, the greatest incidence 

 of coccidia was found in grouse chicks less than three months of age. In this group 10.1 per 

 cent of the chicks were found to be affected. On the other hand only 0.7 per cent of the birds 

 over three months were found infected. A further breakdown of the data indicates that during 

 the first two months, the rate of infection remains alxiul the same, 12.2 per cent and 11.9 

 per cent. The incidence of infection in the birds from two months and older takes a sudden 

 drop to 1.4 per cent and decreases still further until no ex idence of infection was found in the 

 fall and winter months. 



It would seem from tiiis data, that probably a pmnipt infection of susceptible chicks occurs 

 early in life and that an immunity is quickly built up so that subsequent exposure results in 

 little, if any, infection. Tyzzer"' suggested this during his early work on coccidiosis in game 

 birds. The fact that very young chicks feed largely on food on the ground probably accounts 

 for considerable ingestion of oocysts. As the feeding habits of the birds change and less pick- 

 ing is done from the ground, fewer chances for infection occur. 



The relatively low incidence of coccidia and the fact that pathological conditions have not 

 been observed in ruffed grouse as a result of coccidial infections, make it obligatory to exclude 

 these parasites from serious consideration as a factor in grouse mortality. 



Though early grouse breeders" reported coccidiosis to be one of the serious problems en- 

 countered in artificial propagation of recent years, the number of cases observed in captive 

 grouse raised at the Research Center has been almost negligible. 



* Sugar flotation technique. 



