3l4 The Ruffed Grouse 



Michigan, but a corresponding die-off did not occur in the North- 

 east. Leopold and Ball ( 1931 ) generalized the cycle curve for the 

 whole continent but noted several exceptions, among them: the 

 Wisconsin low in 1919 is later than average; in 1905-06 a little ahead 

 of most areas; in 1899 again it is late, this time about two years. 

 Clarke (1936) gives cyclic low periods for Ontario as: 1933-35; 

 1924-25; 1914-16; 1904-06; 1894-95; 1883-85; 1874. These are con- 

 sistently a few years ahead of the dates for the northeastern states. 

 From all the information at hand we may conclude that the geo- 

 graphic lag from Northwest to South and East that is a characteristic 

 of true cyclic species does not hold consistently for ruffed grouse. 



3. The Occurrence of Cyclic Trends in Different Animal Species 

 is Synchronized. 



There is apparently a correlation in cyclic declines of many, if not 

 all, of cychc vertebrate species. When one species of rodent de- 

 clines in an area, others may disappear at the same time. Carnivorous 

 species may decline a year or two after the herbivores decline, after 

 the loss of their food supply takes full effect. Synchronism in the 

 latter case is the result of simple cause and effect: loss of food, 

 loss of life (see Elton and Nicholson, 1942; Chitty and Chitty, 

 1941). Elton (1942), in discussing wild-life cycles in Labrador and 

 Ungava, summarized it thus: "The lemming crashes; the predators 

 crash and migiate; the lemming begins to recover before the slower- 

 breeding predators can catch it up. This is a rough description of 

 a part of a phenomenon that is now known to be generally found in 

 nature . . ." In the case of unfform die-off, it must occur as a re- 

 sult of a common cause acting on more than one species. 



This correlation in population trend between species was well ex- 

 hibited on the Connecticut Hill study area in 19-35-36. Red squirrels, 

 gray squirrels, cottontail rabbits and mice (mainly Microtus) were 

 from seventy-five to over ninety per cent lower in numbers the sec- 

 ond winter compared to the first. Predation was not primarily re- 

 sponsible, nor could significant disease conditions be correlated 

 (although our abihty to diagnose pathological troubles is admit- 

 tedly very limited). No answer was apparent in connection with 

 food, cover, weather, man, or any other matter that could be dis- 

 cerned. The cause, or causes, of this mass decimation remained 

 unsolved. It did, however, show up the simultaneous occurrence 

 of a precipitous decline in several species. The general thought 



