CHAPTER XIII 



FLUCTUATIONS IN GROUSE ABUNDANCE 



By Robert W. Darrow 



OCCURRENCE 



CHARACTERISTICS 



Amplitude — Rate of Change — Duration of Abundance and Scarcity — Periodi- 

 city — Synchronism 



CAUSES 



Relative Significance of Losses During Different Life Periods — Contributory 

 Influences — Predation — Disease — Solar Activity — Weather — Population Density 



CYCLES 



SS 



SUMMARY 



Grouse fluctuate in abundance in all parts of their range. In addition to the constant oscilla- 

 tion of local populations more widespread fluctuations have been reported at periodic 

 intervals, (p. .556) . 



With respect to regional areas there has been a tendency for major declines in abundance 

 to recur at intervals of eight to ten years since 1900 at least, (p. 563). 



Such periods of decline have most frequently occupied two to three years; those of recov- 

 ery three to four years, (p. 560). 



Periods of general abundance sufficient to afford good hunting have usually lasted three or 

 four years, although longer terms have been experienced, (p. 561). 



Major declines in grouse abundance during the years covered have not taken place simulta- 

 neously over its range, nor have recurrent declines followed a regular sequence between 

 regions, (p. .567). 



Pronounced fluctuations at irregular, shorter intervals, often in direct opposition to the gen- 

 eral trend, have been characteristic of local populations, (p. 568). 



Periodic synchronization of the trends of a preponderance of the component local popida- 

 tions of a region seems responsible for the recurrence of general abundance or scarcity, 

 (p. 571). 



