PRODUCTIVITY OF POPULATIONS 



541 



and nesting season. This occurred in spite of the fact that, as shown in table 83, the actual 

 degree of brood mortality recorded also increased as the breeding population rose. On the 

 Adirondack area, however, there was no valid difference*. 



Considering these observations in the light of the fact that the trend in the production ratio 

 has been inverse to that in the number of breeders (table 88) certain inferences may be 

 drawn. On the Connecticut Hill area, with its generally higher population level, losses prior 

 to the brood period appear to have been the stronger influence with respect to the greater 

 average reduction in productivity observed to be associated with higher densities among the 

 breeders. On the Adirondack area, however, even though the net productivity declined as 

 total losses increased with higher densities, the relative importance of the breeding aiid nest- 

 ing season as compared with the brood period did not change materially. At the same time, 

 because the percentage of brood mortality itself has been very similar from year to year on 

 the two areas, the fact that it has represented a greater proportion of the total loss of produc- 

 tivity on this area suggests that the higher nest survival usually experienced in the Adiron- 

 dack region may have been largely responsible for the greater average production ratios 

 recorded. 



Since the relationship of density to productivity may be of major importance in grouse 

 management special efforts were made to evaluate it. After virtually eliminating the birds 

 over 681 acres of coverts adjacent to the Connecticut Hill study area during the winter of 

 1933-34, the population unit was (ielibcrately reduced during each of the succeeding three 

 winters well below what appeared to be its carrying capacity. The data for 1935, 1936 and 

 1937 are compared in talile 90. that for the first year not being comparable because of the 

 rapid influx of birds from surrounding territory'^. 



I XRr.K 00. EFFECT OF HltKKniNCi I'OPHLVTION HKIMICTION ()\ PHODUCTIVITY 



AS OF si;i'ii:\ii5i';u i c.oNNEc.iif.rr mi.i, I'w.i-i'UT 



Several aspects of this record are of considerable interest. Each year the production ratio 

 was greater on the controlled unit than on the basic study area. Furthermore, it increased 

 from season to season as the number of breeders was reduced lower and lower. Yet it in- 

 creased on the check area also until in 1937 the differential between the two was negligible. 

 This, too, was accompanied by a progressive decline in the spring population. In view of the 

 fact that the two productivity rates came closer and closer together each year it is note- 

 worthy that the actual density of breeding birds on the two units followed a similar pattern 

 in spite of their both decreasing. 



Further analysis of the records reveals another significant fact. The season of greatest 

 difference in relative increase, 1935, also witnessed heavy brood losses, apparently as a re- 



* Data were analyzed by clii-squaie. 



A See disrussion of Rale of Spread, p. 522. 



