136 



Game Survey of the North Central States 



The above conclusions and indications are based on the following: 

 Length of Cycle, Wisconsin 



Length 

 between highs 



High 



Low 



Length 

 between lows 



There were three cyclic periods between the low of 1899, the earliest con- 

 clusively dated low for all species, and that of 1927. This covers a total of 28 

 years, which when divided by three gives an average of a fraction over nine 

 years. Three periods between the highs of 1890 and 1923 give an average of 

 exactly 11 years. 



Since, however, the last period is the best supported by evidence and is 

 shorter, the working assumption that the cycle is of uniform 9-year length is 

 followed in the discussions and graphs. It is not considered as proven that the 

 cycle is of uniform length, or that the length is nine years. 



The popular impression that the cycle is seven years long does not neces- 

 sarily contradict the nine-year length here postulated. An "overall" length of 9 

 years would give about seven years between the end of one high or low and the 

 beginning of the next high or low. 



Is Any Territory Exempt? Mortality by Regions. 



(a) No unit of territory as large as a county was exempt from cyclic mor- 

 tality during the last low. (37 out of a total of 71 Wisconsin counties were 

 visited in person, and some information was obtained from every county) . 



(b) The indications are that the last cyclic mortality was universal in all 

 four species throughout the State, but was less severe in the south than in the 

 north, and less severe on thinly populated and isolated range than on thickly 

 populated and continuous range. 



Heavy mortality seems characteristic of large and continuous ranges; lighter 

 mortality on small and discontinuous ranges. No single spot, however small, was 

 found or heard of in Wisconsin where no reduction in numbers had occurred in 

 ruffed grouse and prairie chickens. For these species, and possibly for all species, 

 the cycle appears to have been universal throughout the State. In Michigan and 

 Minnesota, however, it is claimed that a very few small spots suffered no con- 

 spicuous decimation. 



