CAUSES 575 



not been demonstrated in connection with grouse fluctuations outside Ontario. Nevertheless, 

 whatever may be the underlying cause of widespread diminutions in grouse abundance it 

 seems probable that it is usually accompanied by lowered vitality among the young. If 

 this is true, the stage would be set for disease to add momentum to the decline even though 

 the specific organism involved might be different in various regions. 



Solar Activity 



As students continued to ponder the geographic extent of recurrent major fluctuations in 

 grouse abundance as well as their seemingly high degree of harmony they began to look for 

 some all-pervading force as the cause. About this time interest was stimulated in the pos- 

 sibility that variations in solar activity might be correlated with such behavior in wildlife pop- 

 ulations. Using sunspots as an index a relationship between solar activity and terrestrial life, 

 presumably through the medium of rainfall, had been suggested in data on rates of tree 

 growth"". DeLury"' and later Wing"" reported fluctuations in bird migration dates which 

 appeared to correspond more or less to changes in the number of sunspots. Elton'" inter- 

 preted records representing the trends in abundance of several species of birds and mammals, 

 notably varying hare and lynx, as following patterns sufficiently close to the 11.2 year peri- 

 odicity of sunspots to indicate a connection. Here seemed to be the answer — a force capable 

 of causing the continent-wide sweep believed to characterize grouse declines. 



But it has become evident that such a relalionshi]). if it exists at all. is not as simple as 

 at first envisioned. As brought out at the Malamek Conference"" most iSorth American spe- 

 cies, for which the available data indicate some regularity in the intervals between recur- 

 rent fluctuations, have exhibited periodicities of less than ten years which do not correlate 

 with that of sunspots*. MacLulich" later demonstrated this quite conclusively for the varying 

 hare and lynx (Lynx canadensis). Similarly the records for ruiled grouse, to the extent that 

 they represent periodicity, have exhibited an a\erage interval of 9+ years which cannot be 

 directly associated with the sunspot interval of 11.2 years". Furthermore the data of this 

 Investigation and other recent studies, as well as more critical analysis of older records, have 

 shown far less uniformity in the fluctuations of the component populations of a region than 

 was once thought to be the case. 



Nevertheless no one can deny that the sun is the original source of energy upon which 

 the existence of life on the earth depends. Changes in the amount of effective solar energy 

 reaching the earth, although relatively small, are known to take place. Moreover, sunspots 

 are but one manifestation of these changes. Some force not yet recognized may be involved. 

 But, however that may be, there seems little doubt that, if any connection does exist, the 

 motivating mechanism with respect to synchronizing fluctuations in grouse abundance must 

 operate quite indirectly and be subject to considerable variation. 



Several intermediate factors which might function in this way have been suggested. One 

 possibility is that the virulence of disease organisms might vary with changes in solar ac- 

 tivity; another that the vitamin content of food or some other nutritional factor might be 

 affected; still another that some influence associated with climatic or weather conditions 

 might be responsible. Yet little evidence has so far been presented for the first two and 

 even the degree of relationship between weather trends and changes in solar activity is still 

 being debated"' '"• ^"'- "'^. 



* Leopold'^^ has shown a lack of agreement also for the red grouse in Great Britain. 



A Grange'^, using Wisconsin data, has suggested a method of weighting sunspot figures in order to correlate them with grouse 

 abundance but it does not provide for differences such as have occurred between various regions. 



