308 The Ruffed Grouse 



eighty per cent in coverts protected from hunting by man. The dif- 

 ference, thiity per cent of the mortahty, is the nonnal hunting-season 

 loss from gunning. In coverts not well hunted tliis figure may be 

 lower, in overhunted areas sometimes higher. The other one-fifth of 

 the mortality accrues from disease, accidents, and other causes. 



Disease as a decimating agency is difficult to evaluate. Often its 

 effects are obscured by predator action. It is inconsistent in that 

 its importance varies greatly year to year and from one area to an- 

 other. Generally it apparently is not a high or widespread cause of 

 death in grouse. In ordinary years of good grouse abundance, that 

 is years when grouse populations are not rapidly and sharply declin- 

 ing, we estimate that the various diseases and parasite infestations 

 cause from five to ten per cent of the mortality. It is probably 

 greater in imshot range than elsewhere. 



There is evidence that diseases sometimes play a much bigger 

 part in grouse mortality, these usually being years of great decline 

 from peak populations. Allen found that unusually large numbers 

 of grouse died from attack of the gizzard worm on an area near 

 Ithaca, N. Y., in 1926-27 and apparently contributed largely to the 

 cyclic decline that took place. 



In spite of the many organisms that afflict the grouse, many of 

 which can be lethal, we are hesitant in gauging the importance of 

 disease as a factor in grouse mortality. During the period of my 

 observations, no epidemics in grouse were observed. True, there 

 were great variations in the incidence of infestations, the incidence 

 generally rising with the increase of grouse populations. There was 

 also variation in the observed losses from disease in different years. 

 But in no year did we find evidence to show that disease was a mor- 

 tality factor of prime importance. 



Death resulting from mechanical injuries sustained in physical 

 accidents is not uncommon with grouse. Here too, as with disease, 

 the primary cause of death may be obscured by the handling of the 

 bird by predators. Accidents are more common with young adults 

 than with older birds, many occurring during the first autumn after 

 reaching maturity. These early autumn losses are often associated 

 with the "crazy flight" phenomenon (see page 43), and are a 

 function of the fall shuffle of grouse that takes place with the 

 break-up of the family groups. 



As a general rule, accidents usually cause about five per cent of 



