560 FLiCTUATIimS IN GROUSE ABUNDANCE 



Hate of Change 



Of interest also is the rapidity with which grouse aliundaiKC may change to scarcity and 

 vice versa. Considering first areas of regional size, several representative records of declin- 

 ing abundance may be cited. In New York, for example, the last great decline brought the 

 grouse population to a low le\el in 1927 or four years after its high point in 1923, al- 

 though it is important to note that most of the change took |)lace during the years 1926 and 

 1927"'. Similarly the previous low ebb in this State was reached in 1917'' four years after 

 the abundance of 1913. though the birds were still at a high level in 1914. Here again most 

 of the decrease took place during the last two years of the period. On the other hand the 

 marked scarcity of 1907 followed a high level of abundance in 1906" ". A similar pattern was 

 observed over most of the Northeast, except that longer periods were involved in New York 

 (1914-17 and 1924-27) and Pennsylvania (1914-17 and 1924-28) than elsewhere during those 

 decades. 



In Ontario Clarke'^ concluded that "such diminutions have occurred ... in the following 

 years: 1933-4 (and 1935 presumed); 1924-5; 1914-6; 1904-5-6". Two or three year periods 

 of decline were reported from the Lake States between 1914 and 1917, the greatest decrease be- 

 ing experienced in 1916 and 1917. In the following decade the years 1924 to 1926 marked 

 downward trends in Michigan and Wisconsin with the sharpest fall occurring in the last two 

 years of the period. In Minnesota, however, an abrupt drop in abundance took jdace in 1924. 

 Then in 1934 and 1935 grouse populations throughout all three states fell abruptly to a low 

 level after reaching high densities in 1932 or 1933*. Similarly the Lake States experienced 

 major declines within one or two years after the high level of 1942. 



Turning to the rate of recovery grouse reached a peak of abundance in New York in 1935'^, 

 six years after the scarcity of 1927-29, although a high level had been attained by 1934 and 

 in many localities the birds had become numerous by 1932. By 1921 the birds were reported^" 

 to have generally recovered from the low point of 1917 although thev did not reach their peak 

 until 1923, and 1912"" marked the end of the depression begun in 1907. The trend at this 

 time seems to have followed a similar course over most of the New England area. 



Clarke's interpretation of material from Ontario"' indicates that recovery most often occu- 

 pied four or five years but he apparently included (he last vear of the low period. With re- 

 spect to Wisconsin'"' "' the population had regained a high level by 1921 or 1922 following 

 the low of 1916-17. In Michigan'"' "' grouse had become numerous by 1931, four years after 

 the trend started up in 1928. More recently (19401 |Hipulalii>ns ihronghoul the Lake States 

 generally again became abundant after the scarcity of 1934-36. 



One may conclude, therefore, that regional trends have usually involved several years and 

 that the period of decrease has averaged shorter tlum tluit of recovery, although both have 

 exhibited considerable variation. The most frequent intervals of decline have been two to 

 three years in length, with tile sharpest droj) taking place during the last year or two. Recov- 

 ery, on the otlii'r hand, has usually been more gradual, three or four years being the most 

 frequent intervals. 



But a regional population is merely the comjiosite of a host of local populations which 

 may or may not follow similar [)atterns of fluctuation. A knowledge of these local variations 

 is thus of importance also, but unfortunately records of this kind are few. 



• Prt.oniil lonrm lo the nulhots : Kcrilin.-. C. Dr, rmbit T. 1916: l,r.i|inlil. A.. January II. I1.1S ; Ruhl. H. D.. January 21. I9S5. 

 A I hp ralr iil recovery ta iodicatei) liy ihr niinihrr til grouae rcpnrli'd taken by hunlrts rarli year aince ihr cloaed aeaaona nl 

 1928 and 1929 ai followa: 1930. 37,188; 1931. 40,448; 1932. 55.845; 1933, 63,910; 1931. 81.614; \t:is. l;«..30l. 



