
comparable sample areas indicate that the decrease in breeding population 
may have been in the neighborhood of 30 percent. There is little question, 
however, but that there was a decrease in the size of the breeding population. 
Production indices 
An aerial production survey was conducted in North Dakota 
first time this year. The results are presented in Table 4. 
Table 4 = Summary of North Dakota Aerial Survey Data, July 1957 


Strata State 
__West —__—- Central East — Totals — 
Size in square miles | 23,474 33,861 13,330 70,665 
Sample size in square miles 36 147.4. 17 200.4 
Broods actually seen 7 5 126 - 9 140 
Broods per square mile 0.14 0.85 0.53 0.7 
Brood Index =” | 3,260 28,942 7,056 39,258 
PLB actually seen | 8 171 3 - 
PLB per square mile |. 0.22 © 1,16 0.18 © 256 
Late nesting index 5,215 39,277 2,352 46, 844 
Ponds actually seen 110 681 34 = 
Ponds per square mile 3.0 4.65 — 2 2.8 
Pond Index 71,720 100, 379 26,656 198,755 
Coot brood seen 0 43 a ae 
Coot broods per square mile 0 0.3 0.12 | - 
Coot Brood Index 0 9,877 1,568 11,445 
Late Nesting Index by Species 
Percent 
Species West Central East State .§ Comp. 
Pintail = 2,297 ~ 2,297 5.0 
Mallard 2,086. 19, 754 1,176 23,016 49.1 
Baldpate - | 459 Rhee 459 1.0 
Shoveler fe PhS eee, 689 - 689 1.5 
Gadwall oe a 2,756 2,756 5.9 


Continued ae 
54 
