578 FLICTUATIONS /A GROUSE ABi\DA.\CE 



CYCLES 



No discussion of fluctuations in wildlife abundance would be complete without including 

 the concept of cycles. Ever since observers began to realize that the interval? between suc- 

 cessive periods of abundance and scarcity of many species had exhibited a tendcncv toward 

 regularit) , the idea of their recurring in cycles has appealed to scientist and sportsman alike. 

 It has appealed particularly to those interested in game because it suggests the possibility 

 that the future course of abundance can be predicted. For this reason it is important to 

 "look at the record," especially with reference to grouse, to see how strongly existing data 

 support this hypothesis. 



The concept of cyclic behavior is not new. Since the begiimings of time the cycle of 

 night and day, and the annual cycle of the seasons have been recognized. During the past 

 two centuries, however, cycles have been ascribed to a great many other things. Probably 

 the best established, aside from the movements of various celestial bodies, is that of the 

 changes in the sun represented by sunspots. Closely associated with this are the variations 

 in terrestrial magnetism, while less well correlated are fluctuations in ultra-violet radiation 

 from the sun and climatic changes'. But cycles have also been described in such things as 

 the price of common stock, building activity, tlie prciduction of pig iron and death rates from 

 various diseases'". With respect to wildlife, abundance data have been interpreted as indi- 

 cating cyclic behavior among a variety of species chiefly in the northern hemisphere. Among 

 them, in addition to the ruffed grouse, may be mentioned mice and lemmings'"' '"', varying 

 hare and lynx^'", the arctic fox (Alopex lagopusJ''\ the red grouse (Lagopus scoticus) in 

 the British Isles"" and the Atlantic salmon (Salino salar)'". 



A significant feature about these fluctuations, however, is the variety of periodicities rep- 

 resented. For example, the ruffed grouse seems to have exhibited an average interval between 

 peaks and troughs of slightly more than nine years*. MacLulich"'" concluded that those of the 

 varying hare and lynx were both 9.7 years and Elton'" found approximately the same peri- 

 odicity in the records of the Hudson's Bay Company for the muskrat (Fiber zibelhicus), red 

 fox, marten I Maries americana) , wolf (Canis) and mink (Muslela vison). An interval of be- 

 tween nine and ten years has been reported also for the Atlantic salmon""". On the other 

 hand, mice, lemmings (mainly Leininus trimucronaliis) and the arctic fox iiave followed 1- 

 year trends in North America and Europe'^'- '". Tluil of liie red grouse in Britain has av- 

 eraged 0..5 years"", while its cousin, the willow grouse or rype I Lagopux lagopus) of Scan- 

 dinavia, has shown a pattern of three to four years'". The sunspot cycle has a mean of 

 11.2 years, while agricultural productivity in the I'nited States, which would sccni to reflect 

 climatic changes, has shown a 18.6-year fluctuation'"'. 



But. irrespective of the periodicity involved, none of these trends has exhibited a precise 

 recurrence of its successive peaks and troughs. The degree of variability in this respect has 

 differed considerably between species, in man) cases being quite wide. The intervals seem 

 to have been most nearly constant among the mice and Irnmiings as well as the arctic fox. 

 Other species have varied to a greater extent. i"oi ihc lulled grouse from seven to twelve 

 years have elapsed between "highs" in different instances and from eight to eleven years 

 between "lows". This frequency has ranged from eight to eleven years for the varying hare 

 and from eight to twelve years for the lynx. In the case of the red grouse in niilain it has 

 Naried from four to eight years. But even the reconiic! Ilmlualions in >uris]>ots have shown 

 a variable recurrence of from seven to seventeen years. 



• Sec (liscuaaiiin <■( (•.■ri.iili. ilv, p. .Id:!. 



