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MAJOR BIRD STUDIES 



CANADA GEESE STUDIES 



Investigations into the ecology of Canada geese on the lower 

 Yellowstone River were divided into six periods: wintering, spring migration, 

 breeding, brood-rearing and flightless, early fall resident, and fall 

 migration. The wintering period began with the onset of extended periods 

 of cold weather in late fall which induced geese in most sections of the 

 river to depart on southern migrations, possibly because of extensive ice 

 cover on the river. Wintering periods ended with the onset of warmer 

 weather, the resultant ice melt, and arrival of migrants in early spring. 

 Thus, the spring migration period begins as migrants stop in the study 

 area on their way to northern breeding grounds and ends as most migrant 

 flocks present in the study area dissipate. The early part of the breeding 

 period overlaps with the end of the migration period, in that the establish- 

 ment of territories by resident birds occurs while some spring migrants are 

 present in the same areas. The breeding period ends and the brood-rearing 

 and flightless period begins when the first clutches hatch. This period 

 ends and the early fall resident period begins when the first flocks of geese 

 gain flight. The early fall resident period extends through the fall until 

 the first cold and snowy weather brings large numbers of migrant geese 

 back into the area. The fall migration period continues until the onset of 

 cold, wintry weather. 



Wintering Period 



Geese Present . Numbers of Canada geese observed in the study area during 

 this period in 1975 and 1976 were among the lowest observed during the study 

 (figure 4). Only during the brood-rearing and flightless period were the 

 censuses as low, but during that time geese are secretive and difficult to 

 observe from the air. During the wintering period, 83.8 percent of goose 

 observations recorded during aerial censuses occurred between Bighorn and 

 Hathaway (table 1). Study sections within that reach remain largely free 

 of ice because of the entrance of warmer water from the Bighorn River into 

 the Yellowstone and its influence on ice formation downstream. Below Miles 

 City, the river was largely frozen during the winters of 1974-75 and 1975- 

 76 and did not harbor a significant number of geese (table 1). 



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