Productivity and Populations 295 



usually from one hundred to three hundred acres each ) , we do find 

 greater variation in grouse densities from year to year. Some units 

 increase their group populations from one year to the next while 

 others decline. Summation of these records for the whole area tends 

 to average out tliese irregularities. These records for individual 

 coverts are of interest primarily in showing the potentialities of the 

 different coverts for producing and holding grouse. Some show a 

 particular abilitv to produce giouse, i.e., high summer productivity, 

 others to hold them over fall and winter until the breeding season. 



Extremes of breeding season densities of single cover units range 

 from less than four to almost fifty acres per grouse. Areas that reach 

 the greatest densities in their highest years, have relatively high den- 

 sities in their lowest years; those with low densities in poor years 

 also have a low density even in the best years. The primary key to 

 the spring density of levels of cover imits lies in the winter shelter 

 (primarily evergreen cover) conditions. 



The cover units that provide the extremes of peak population 

 densities are not usually the same as give the corresponding ex- 

 tremes in breeding population densities. The greatest density of 

 grouse at about September 1 in a single cover unit was a grouse for 

 every one and eight-tenths acres (N. Y. S. Cons. Dept. Ann. Report, 

 1935), while the lowest peak density was less than one to thirty 

 acres. 



These extremes, together with all the other year-to-year records 

 of individual coverts, show clearly that animal populations are very 

 dynamic, ever changing, and, barring occasional losses that prevail 

 rather uniformly over large areas as a result of some climatic factor, 

 are normally little related to other populations even a short distance 

 away. General increases and decreases in population, such as we 

 have discussed for a whole area, are merely the summation of these 

 individual unit trends. When the majority of units are increasing in 

 population, the whole area will probably show an increase; when 

 the majority are declining, the net total is likely to decline too. And, 

 as already noted, the population fluctuations for a whole area are 

 less violent than those of the individual component coverts, for, as 

 we make the summations, the individual gains and losses will cancel 

 each other to some extent. 



Population densities on other areas have shown as much varia- 

 tion from Connecticut Hill as have the individual cover units among 



