on the main bank in sagebrush cover near the mouth of a creek. Territorial 

 baldpate and gadwall drakes loafing on the river in these areas suggested that 

 hens of these species were also nesting nearby. 



Wood duck broods were observed in backwaters between Billings and Savage. 

 All mallard broods observed occurred between Billings and Miles City. The 

 paucity of observations of dabbler broods is believed related to the need of 

 dabbling ducks to rear their young in lentic habitats where duckling foods are 

 plentiful (Sugden 1973). These lentic water areas in the river valley consist 

 of old oxbows, stockponds, marshes, roadside sloughs, and railroad ditches. 

 The flowing water of the Yellowstone proper is probably marginal dabbling 

 duck brood habitat. 



Sex Ratios 



Flocks of mallards present in the study area during late fall were composed 

 of from 62.5 to 65.3 percent drakes (table 15). Bellrose et al . (1961) trapped 

 black and mallard ducks in Illinois during the fall from 1939 to 1950 and found 

 between 60 and 73 percent drakes in these samples. Sugden et al . (1974) found 

 70 to 73 percent drakes in flocks of mallards overwintering near Calgary, 

 Alberta. Drewien (1968) reported 75 percent drakes in a sample of mallards 

 trapped in northwestern South Dakota in the winters of 1950-51 and 1951-52. 

 Bellrose et al . (1961) suggests the sex differential in mallard populations 

 favoring drakes reflects differential migration of the sexes and higher 

 mortality of hens during the breeding season. 



TABLE 15. Proportion of drakes in mallard flocks along the lower Yellowstone 



River, 1974 and 1975. 



Number of Number of Total Proportion 

 Date River Section Drakes Hens Sample of Drakes 8 



11/30/74 Miles City to Fallon 1,998 1,061 3,059 65.3 

 11/30/74 

 to 



12/11/74 Rosebud to Miles City 1,064 624 1,688 63.0 



11/30/74 Sanders to Rosebud 1,424 836 2,260 63.0 



11/30/74 Myers to Sanders 2,137 1,165 3,302 64.7 



11/25/75 Sanders to Forsyth 1,161 697 1,853 62.5 



Expressed as a percentage 



COMMON MERGANSERS 



Numbers of common mergansers {Mergus merganser) observed in the study area 

 were highest from late fall through early spring (figure 20), which reflected 

 the presence of wintering populations, most of them upstream from Miles City. 



53 



