early fall migrants. Censuses of geese in the study area at this time showed 

 between 1,500 and 3,500 birds. Most field-feeding geese were observed in winter 

 wheat fields in the early part of this period and in barley and corn fields after 

 these crops had been harvested. Loafing geese utilized open bars and islands as 

 they had in late fall and early spring. Observations of neck-banded individuals 

 in early fall indicated the tendency of geese to limit up- and downstream 

 movements along the river, which later became apparent at other times of the 

 year as well . 



Goose censuses in the study area during the fall migration period 

 occasionally totaled over 10,000. During this period geese fed most commonly 

 in barley, wheat, corn, and hay fields. The largest concentrations of geese 

 at this time occurred in the area between Bighorn and Kinsey, one of the more 

 heavily-utilized migration corridors in this section. 



No statistically significant correlations were found between the numbers of 

 geese counted at a given time of year in a section of river and the morphology 

 or vegetation of the river in that section. The characteristics measured from 

 aerial photographs included the number of islands, sinuosity, area of gravel 

 bars, and the area of agricultural land, cottonwood-grassland, and dense 

 cottonwoods in each section of river. 



DABBLING DUCKS 



Numbers of dabbling ducks observed during aerial counts were highest during 

 spring and fall migration periods (sometimes exceeding 45,000) and lowest during 

 brood-rearing and late summer. Mallards were the most common dabbling ducks 

 present in the study area. Field-feeding species utilized picked cornfields 

 most heavily throughout the study period. Sections of the river with an 

 abundance of secure loafing sites, water, and nearby picked cornfields 

 attracted the largest numbers of dabbling ducks. 



Nesting dabbling ducks were located on a few occasions but generally appeared 

 to be uncommon along the mainstem Yellowstone. Dabbling duck breeding populations 

 were thought to be limited by the paucity along the main channel of lentic water 

 areas necessary for brood rearing. 



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

 of from 60 to 65 percent drakes. 



Mallards overwintered in the study area, largely in the open water stretches 

 used by overwintering Canada geese. 



OTHER BIRDS 



Common mergansers were present year-round in the study area but were most 

 numerous during the winter. Most were observed between Billings and Miles City, 

 possibly because of more productive fishing in that section. Merganser stomachs 

 examined for food contents revealed utilization of stonecats and goldeneyes. 

 Observations of merganser broods showed that they do nest on the river, although 

 no nests were actually located. 



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