322 The Ruffed Grouse 



eastern states that the bird's ability to reproduce is periodically 

 lessened. King advises (letter, October 5, 1943) that he did find 

 evidence of this condition in Minnesota. 



SUMMARY OF ANALYSIS OF PERIODIC FLUCTUATIONS 



From all of the information available and from the field studies I 

 made, the following conclusions seem to be warranted: 



The ruffed grouse undergoes marked periodic changes in popula- 

 tion over its optimum range. These fluctuations are not sufficiently 

 regular to be caused directly by some all-pervading common cause. 

 They are inconsistent geographically, both in time of occurrence and 

 severity of action. The supposed Northwest to Southeast lag is not 

 consistent. The decimations that annually occur, whether normal or 

 abnormal, are the product of the interaction of environmental fac- 

 tors, primarily weather conditions, parasite and disease infestations, 

 and predation. These factors are conditioned by the habitat, by 

 variations in climate ( including sunspot cycles ) and, in some areas, 

 to a minor extent by man. These factors may individually or col- 

 lectively go berserk on occasion with resulting catastrophic losses of 

 grouse. The effect on grouse is sometimes felt only after a chain of 

 connected events is set up with other animals, such as the rodent 

 loss = predator's food scarcity == shffted predator pressure chain. 

 The rodent declines may be set up by food scarcity, may be con- 

 nected with chmatic factors, and are probably not directly correlated 

 with sunspots. 



Grouse naturally have a high potential productivity which results 

 in high populations in favored years. High breeding densities then 

 lead to poor recoveries through high losses in young birds. This 

 mechanism, whatever may be the immediate decimating agencies, 

 seems basic to the periodic losses in this species. Further, this phe- 

 nomenon is not assumed from individual year's records, but is shown 

 to follow in series of years. It seems to have three phases, one of high 

 recoveries from moderate breeding populations, a second of poor 

 recovery from a high breeding population, and third, in occasional 

 periods, a continued poor recovery from low breeding populations. 

 Irregularity is a normal characteristic of grouse population changes. 



Cause of grouse die-offs cannot be traced to a single source. 

 There is no simple answer. It is the result of a complicated interplay 

 between a multitude of natural factors and many kinds of organ- 



