PARASITISM AND DISEASE IN WILD GROUSE 413 



the infection is gained by eating ants, which early in the summer form a large part of the 

 animal food of the chicks. Coccidia, which have a direct life cycle, are obtained by accidental 

 ingestion of the infective stages during feeding. Neither coccidia nor the above tapeworms are 

 found in any appreciable number of adults. Ticks, which occur on about 12 per cent of both 

 chicks and adults during the summer, are most frequent in July. 



During July, the three parasites which occur most frequently in adults begin to make 

 their appearance in the chicks. These are the stomach worm (Dispharyii.x spiralis) gizzard 

 worm I Cheilospirura spiuosa) and intestinal worm ( Ascaridia bonasae). In the birds of the 

 year during the fall and winter, the stomach worm occupies a prominent position. Although it 

 seems capable of producing lesions equally serious in adults as in young birds, the relative 

 incidences probably indicate its greater importance in the latter. 



Yearly Variations 



In view of the numerous reports on the cyclical nature of grouse abundance and scarcity, 

 the analysis of the data on parasitism on a yearly basis was regarded as one of the most im- 

 portant phases of the Investigation. 



Although, in some instances, superficial inspection of the data seemed to indicate that yearly 

 variation occurred, this was found to be due largely to changes in the intensity of collecting 

 in localities or seasons in which the parasite might be more or less abundant than the average. 



Since these seasonal and regional effects had to be removed in treating the material, the in- 

 cidence of only the numerously occurring parasites could be compared from year to year. 

 These analyses were carried out for intestinal roundworms, stomach worms, gizzard worms and 

 tapeworms in adults and for tapeworms, intestinal roundworms, stomach worms and ticks in 

 chicks. 



No evidence could be adduced to support the idea that significant changes in the incidence 

 of parasites took place from year to year during the course of the Investigation. It must be 

 remembered, however, that no substantial decline in the grouse population occurred during 

 this period. 



Seasonal Variations 



The general view that disease and parasitism is more prevalent during the warmer months 

 is borne out by observations on tapeworms and intestinal worms in grouse, but it is not appa- 

 rent from the data on stomach worms. No explanation for this difference is suggested by the 

 data or the facts which are known concerning the parasites and their method of dissemina- 

 tion. The drop in incidence of coccidia from 12 per cent in July chicks to less than two per 

 cent in fall juveniles is probably attributable to age and iinniunity rather than season since 

 the incidence in summer adults is also very low. 



Regional Distribution 



Analysis of the data on parasites taken during the Investigation reveals three salient exam- 

 ples of regional distribution of the parasites observed. A higher incidence of ticks was found 

 in the Adirondack region. In the same region, an exceedingly low incidence of stomach 

 worm was noted. Autopsies revealed no records of crop worms outside of the Hudson Valley. 

 With the exception of these three instances, the distribution of the parasites was statewide. 



It should be pointed out here that the figures used in comparing the tick populations on 

 "rouse in the various regions of the State have been based only on those specimens taken by 



