IvtttodctCtiCM 



PURPOSE 



The purpose of the study was to determine the importance of the 

 Yellowstone River to geese, ducks, bald eagles, great blue herons, and other 

 migratory birds and assess the impact on those birds of altered streamflow. 

 The structure and vegetation of the river, with particular attention to 

 islands, were also to be studied. 



SCOPE 



Although all large migratory birds present in the study area were 

 studied to some extent, more time was invested in observation of the most 

 common species. Canada geese (Branta canadensis) were believed to be the 

 only large migratory birds to breed, rear their young, summer, winter, and 

 occur as fall and spring migrants on the lower Yellowstone River. Because 

 of this year-round use of the river and of the species' economic and 

 aesthetic value, goose studies were given the most time. Mallards {Anas 

 platyrhynchos ) were also believed to occur in the study area year-round, 

 but nesting and brood-rearing on the river itself was thought to be limited. 

 Great blue herons {Ardea herodias) were known to nest and rear their young on 

 the river but were not believed to be present during the colder months of the 

 year. Bald eagles {Haliaeetus leucocephalus) had been observed along the 

 river during the colder months but were not believed to breed there. All 

 other migratory birds were ranked below these in importance in the study. 



In the analysis of river structure and vegetation (conducted from 

 aerial photographs), the parameters studied were cover type, length of shore- 

 line per cover type, island size, thalweg length, sinuosity, total water area, 

 total shoreline length (wetted perimeter), and total gravel bar area. 



STUDY AREA 



To permit more intensive study of large migratory birds in areas where 

 they were believed to be more numerous, the study area was limited to the 

 Yellowstone River from Billings to the North Dakota border. The analysis of 

 vegetation was also limited to that section of the river to allow comparison 

 with the numbers of birds observed. 



Other geographic limitations involved local variations in habitat use 

 by particular species. Duck, goose, and bald eagle feeding areas, for 

 instance, included the largest area. Most observations of the other birds 

 were limited to the river banks, islands, and channels. 



