and management of riparian ecosystems (Johnson and Jones 1977, Johnson and McCormick^ 

 1978), and a similar symposium was recently held in Colorado (Graul and Bissell 1978^^ 

 While the cottonwood-wil low riparian ecosystem is "unquestionably the most produc- 

 tive and highly diversified ecosystem in the west" (Beidleman 1978), it is also our 

 most endangered nabitat (Mustard 1978). 



Many stjdias have documented that the high structural diversity and horizontal 

 patchiness of multi-layered riparian forests contributes not only to greater numbers 

 of birds, but also to a greater diversity (both of species and guilds) than most 

 other temperate habitats (Wal check 1969, 1970, Carothers et al". 1974, Thompson 1978, 

 Meslow 1973, Anderson, et al . 1977). In the present study, both the breeding bird 

 census and riparian habitat transects showed that riparian trees and shrubs support 

 both more individual birds and a greater variety of birds than any other habitat 

 studied. 



Riparian forests and shrubbery are highly productive, and those in the study 

 area probably have a ne: primary productivity on the order of 5-10 tons/acre (Golden 

 et al . 1979). Much of the production is in the form of browse available to white- 

 tailed deer, and loss of this habitat would probably reduce w.ii te-tailed deer carry- 

 ing capacity. Deer security within the riparian habitats which would be flooded 

 along the south bank of the river is presently limited by existing disturbances in 

 the area, notably traffic on the twin railroad tracks, the unimproved road parallel- 

 ing the tracks. Highway 2, and fishermen and sight-seer traffic. In fact, few deer 

 were seen in this area during the study. 



Both the riparian deciduous forests and the coniferous forests provide perch 

 sites and potential nest support structures for osprey and bald eagles. The trees 

 that would be removed do not appear to be preferred or specially selected by these 

 birds. Available data indicate that wintering bald eagles use whatever tall trees 

 are available close to the river's edge (especially within 15.2 m (50 ft)), and that 

 after impoundment the availability of suitable roosting or nesting trees would not 

 be reduced. 



The forest types which would be inundated or cleared are a source of snags and 

 dead or decaying trees, which are important as nest sites or feeding sites for a 

 variety of species. Many recent studies have shown the importance of snags and old 

 growth to cavity-nesting birds and mammals (Meslow 1978, Bull 1978, McClelland 1977, 

 Jackman 1974); cavity-nesting species found in or near the study area 

 are listed in table 22. Loss of existing snags, and of a source for future snags, 

 would represent a significant, long-term loss for these species. 



A total of 1.2 ha (2.9 acres) of riparian grasslands and hayfields would be in- 

 undated assuming a forebay of 610 m (2,000 ft). These habitats are relatively scarce 

 in the area, and support relatively high densities of rodents. Of the 1.2 ha (2.9 

 acres) affected, almost none occur on the north bank of the river adjacent to big- 

 horn sheep concentration areas (Figure 8). However, the rise in water table brought 

 about by the pool is likely to encourage establishment and growth of hydrophilic 

 shrubs over a much larger grassland area, thus reducing further the amount of for- 

 age available to bighorn sheep. Bighorns use these low-elevation grasslands most 

 heavily in spring, preferring such grass species as Festuca scabrella , Festuca 

 idahoensi s, A^ro^yron spicatum, Koeleria cristata, and Stipa c omata in the nearby 



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