COMMON GOLDENEYES 



Common goldeneyes {Bucephala clangula) ,like common mergansers, were most 

 numerous on the lower Yellowstone from late fall through early spring 

 (figure 21). The higher peak numbers present in the winter of 1974-75 

 were the result of concentrations of goldeneyes between Pompey's Pillar and 

 Forsyth. Those concentrations did not occur in the winter of 1975-76, 

 possibly because warmer weather that season induced goldeneyes to winter 

 further north. Goldeneyes were not observed during aerial censuses conducted 

 from late spring through fall each year (figure 21) and are not believed to 

 breed in the area. 



Goldeneyes were sometimes observed loafing and feeding with common 

 mergansers. Flocks of goldeneyes were observed flying upstream, drifting 

 with the current, diving to feed, and returning upstream to resume feeding, 

 as were flocks of mergansers. Goldeneyes commonly fed in the deep water of the 

 main channel and along ice shelves at the water's edge in winter. The two 

 goldeneyes collected for food habits analyses had eaten aquatic plants and 

 invertebrates (appendix B). 



BALD EAGLES 



Bald eagles Haliaeetus leucooephalus) were present in the study area from 

 September through April in 1975 and 1976 (figure 22). One pair attended a nest 

 on the river near Sanders during June of 1975 and 1976, but close aerial 

 observation of that nest in mid-June 1976 revealed no eggs or young present. 

 This pair was the only bald eagles observed in the study area during the time 

 of year that bald eagles normally raise young. Peak numbers of eagles were 

 present during migration periods, late fall and early spring. 



Twenty-nine percent of the bald eagles observed during aerial censuses 

 throughout the study were classified as juvenile birds. Sprunt and Ligas (1963) 

 reported 26.5, 23.7, and 21.6 percent juveniles in the continental bald eagles 

 population in 1961, 1962, and 1963, respectively. Along the lower Yellowstone, 

 the highest percentages of juvenile eagles in the population occurred in 

 late December 1974, mid-to-late March 1975, and mid-March 1976 (excluding 

 those censuses conducted when the number of eagles present was very small). 

 The lowest percentages of juvenile eagles occurred in early December 1974, 

 January and February 1975, and during the winter months of 1976. Thus, 

 juvenile bald eagles appeared to comprise a high percentage of the migrant 

 population and a low percentage of the overwintering population. 



Bald eagles were observed throughout the study area, but 76 percent of 

 those observed during aerial censuses occurred between Billings and Miles City. 

 Concentration of eagles in the western half of the study area may be related 

 to the river's being frozen downstream from Miles City during much of the 

 period when bald eagles were present in the valley. Those stretches which 

 were devoid of open water and flocks of ducks seemed to be avoided by eagles. 

 During colder periods, when ice cover in the upstream sections was extensive, 

 those reaches where open water was common and duck flocks present seemed to 

 attract most of the eagles observed. These factors are believed more influential 

 in determining bald eagle distribution along the river than any morphological 



56 



