194 
Duck Brood Densities and Distribution 
The brood densities observed during this survey appear in Table IV. Over 
the East River Country as a whole there was an observed brood density of 0.71 
broods per square mile. The highest observed density was in the Prairie Hills 
which averaged 1,04 brood per square mile. The James River Valley ranked 
second with 0.72 brood per square mile; and the Missouri Hills third with 0.48 
broods per square mile. No broods were observed in the Minnesota Valley, but 
this was undoubtedly due to the effect of chance in the small sample. 
Table IV. - Observed Duck Brood Densities in Eastern South Dakota 

Minnesota Prairie James River Missouri East River 
Valley Hills Valley Hills Totals 
Sq. Miles Sampled 9.2 85.3 166.3 70.3 331.1 
Broods Observed 0 89 113 34 236 
Broods Per Sq. Mi. 0.0 1,04 0.72 0.48 0.71 
It should be noted that the observed brood densities listed above are only indexes 
to brood densities. These indexes are considerably lower than the actual brood densi- 
ties because a large portion of the brood present are not observed. At present these 
brood indexes are of little use in evaluating duck production because similar indices 
for previous years are lacking. Their only immediate value is to show the importance 
to over-all duck production of such areas as the James River Valley and Missouri 
Hills. The indexes in Table IV show that the highest brood density occurred in the 
Prairie Hills, and that the brood densities in the James River Valley and Missouri 
Hills were 70 percent and 46 percent as high as in the Prairie Hills. The areas of 
these physiographic divisions are: 8,107 square miles in the Prairie Hills; 18, 784 
in the James River Valley; and 7,579 in the Missouri Hills. The product of the area 
and the brood density index of each division is an index to the minimum number of 
broods in each division. Thus, at the time of the survey there were at least 8, 400 
broods in the Prairie Hills; 13,500 in the James River Valley; and 3,600 in the 
Missouri Hills. There were 61 percent more broods in the James River Valley and 
57 percent fewer broods in the Missouri Hills than there were in the Prairie Hills. 
The James River Valley and the Missouri Hills combined contained more than twice 
as many broods as did the Prairie Hills. 
