312 The Ruffed Grouse 



that these long-term variations in temperatures, precipitation, and 

 other weather factors affect tree growth (Douglass, 1941), as they 

 logically would. There is considerable evidence that sunspot cycles 

 are related to changes in population of some rodents, of migratory 

 salmon, and other animals. The relationship may be indirect, through 

 the effects on environment or climate; or it is conceivable that it 

 may bear some direct relationship, as yet not imderstood. It is now 

 well-known that simspot activity affects our radio waves. Who are 

 we to say that these changes in solar radiation may not directly af- 

 fect forms of Iffe on the earth, with animals dependent on vitamins, 

 hormones, and what not? One author has even gone so far as to cor- 

 relate wars and business cycles with sunspots (Stetson, 1937). 



Now what is the evidence supporting and refuting the existence 

 of giouse cycles, and what conclusions may we draw? 



That there are fluctuations— and wide too— in grouse numbers 

 is well-known. Clear and fairly complete records of years of abun- 

 dance and scarcity go back to 1904 for some areas, notably the 

 northeastern states. Scattered records indicate certain years of 

 scarcity or abundance for some areas back as far as the late 1860's, 

 and inferences may be drawn from a few writings prior to that 

 time. But until the studies of the last two decades, little reliable in- 

 formation was available on the population mechanics of tiie bird. 



Mere fluctuations in population of a species does not in itself 

 indicate any tendency to a cyclic behavior. All species are constantly 

 changing their numbers, not only in detail but often in general 

 sweeping surges. On the mathematical law of probabflity, when a 

 species has a high population level (for its kind), it is most likely 

 to decline in numbers; and conversely, when it is scarce (but not 

 below the tlireshold of satisfactory mating), it is most likely to in- 

 crease. This is one more case of the natural law of biological equi- 

 librium commonly referred to as "the balance of nature." 



In order to evaluate the evidence on grouse cycles, let us now 

 consider the many causes, features, and characteristics of cycles 

 and see how they fit into our knowledge of Bonasa umbellus. 



1. Peaks and Troughs of the Cycle are Regularly Spaced in Years 

 in any One Portion of the Continent. 



Years of scarcity of grouse in the Northeast are well documented 

 for 1927-29, 1924, 1915-17 (Stoddart, 1918), 1907 (Forbush, 1912), 

 1904 (Forbush, 1912), 1896-97 (Dillin, 1920). There is some evi- 



