currently have little agricultural development near the river (e.g., near the 

 mouth of the Powder River and between Terry and Fallon) and least apparent 

 where extensive agriculture along the river is now present (e.g., near Huntley 

 and Sidney). Attraction of field-feeding waterfowl to the Yellowstone Valley 

 could be further enhanced by the development of circular sprinkler irrigation 

 systems. Eagles could conceivably benefit from increased duck and goose 

 concentrations, as well as from an increase in feedlots and livestock pastures 

 on the river bottom, providing greater numbers of animal carcasses on which 

 they could feed. 



BIGHORN RIVER 



Water withdrawals from the Bighorn could exaggerate the channel changes 

 which have already occurred there since the closing of Yellowtail Dam in 1965. 

 Changes which could occur include a further restriction of the flow into one 

 main channel, stabilization of bars and islands, accelerated vegetational 

 succession, and an increased rate of loss of islands. 



The island loss and vegetational succession which has occurred since the 

 Bighorn's regulation (Martin 1976) may have produced a demand for secure 

 goose nesting sites. Further loss of island and progression of vegetational 

 succession would probably reduce the goose breeding population further through 

 loss of nest sites and competition for the few remaining sites. Loss of 

 islands would also result in lower numbers of island-nesting ducks and 

 mergansers. 



Aspects of fish concentrations brought about by reduced water levels 

 would probably resemble those in the Yellowstone River. Short-term reductions 

 could benefit eagles, cormorants, mergansers, herons, and other piscivorous 

 species but harm these same species if the fish habitat was reduced for too 

 long. 



Further agricultural development in the Bighorn Valley could increase 

 feeding areas for migrant ducks and geese. Flocks arriving in the fall may be 

 induced to winter along the Bighorn below Yellowtail due to the presence of 

 open water and abundant food sources. Sudden winter storms followed by extreme 

 cold could produce abnormally high mortality in those wintering populations. 

 Large concentrations of those species could also suffer increased mortality 

 through spread of diseases. Increased agricultural activity in the Bighorn 

 Valley could provide for more feedlots and livestock pastures along the river, 

 increasing the attraction of eagles to carrion in those areas. 



Goldeneye populations on the Bighorn could be benefited by extensive areas 

 of open water through the winter. However, any water withdrawals which decrease 

 the populations of bottom-dwelling invertebrates or algae upon which goldeneyes 

 feed could also decrease their population levels. 



73 



