The project-t^elated features which would most likely cause displ,. cement 

 of animals are: (1) the presence of up to 500 construction workers in the 

 project area; (2) construction activity in the dam area, outlet area, and the 

 work area at the head of the Falls; (3) blasting noise during excavation; 

 (4) noise created by transport and unloading of excavated material; (5) noise 

 created by clearing machinery, earth-moving machinery, concrete plants, and 

 other on-site machinery. Construction would extend over a 4.5 yr period, 

 with most of the excavation and railroad relocation taking place during the 

 first 18 months (NLI 1978), Estimates of noise levels to be created oy this 

 project are not available from NLI, but similar types of activities can be 

 expected to produce noise levels of 78 - 88 dB with occasional peaks of llOdB 

 at a distance of 15.2 m (50 ft) (Golden et al . 1979). 



The wildlife species of the project area which would be i.^'ost sensitive 

 to construction noise and human activity are waterfowl, large raptors (espe- 

 cially the ba"'d eagle), and ungulates. Waterfowl would probably avoid the 

 entire pool area during construction and dumping of fill along the south 

 shoreline. Harlequin ducks are particularly sensitive to human disturbance 

 (Kuchel 1976), and would be displaced fromthe Falls during dam construction. 

 Wintering bald eagles are also wery sensitive to hunan activity (Craighead 

 and Craighead 1979, Meyer 1979), and would probably avoid the stretch of river 

 from the outlet to near the pool head during construction. At present, the 

 Falls area is the portion of the Libby-Troy section of the river most heavily 

 used by bald eagles (Meyer 1979). Bighorn sheep would initially avoid the 

 Falls area during construction, probably moving into less suitable habitat 

 farther upslope, but would probably eventually become habituated to some 

 extent and return at least partway. Bighorns are apparently able to habituate 

 readily to constant or regular disturbances, and presently occupy the area in 

 spite of noise from the Falls, the railroad, and from traffic on Highway 2. 

 The few white-tailed and mule deer present in the project area would be dis- 

 placed during construction. 



With the exception of the harlequin duck, all species displaced by con- 

 struction disturbances would probably return following completion of the pro- 

 ject (to the extent that suitable habitat remains), and are unlikely to suffer 

 long-term population-level effects as a result of displacement. Little 

 opportunity exists for mitigation of noise and construction related displace- 

 ment, other than seasonal curtailment of construction, as mentioned below. 



CHANGES IN MORTALITY AND NATALITY RATES 



Minor variations in the natural mortality rate of a population are normally 

 balanced by over-production of young or, in many cases, by an increase in the 

 natality rate, with the result that most animal populations are maintained at 

 or near carrying capacity. Thus, increased mortality rates or decreased natality 

 rates have a serious significant impact on populations only when they exceed the 

 potential of the population to recover. If mortality rates increase or natality 

 rates decrease for long periods of time, a population can become locally extinct. 

 Small mammals and other r-selected species have high reproductive potentials 

 and high natural mortality rates; very high mortality in populations of these 

 species can often be compensated for in a few months or years. Species most 

 likely to exhibit population-level effects of increased mortality are those with 

 a low reproductive potential, those which are already rare or in danger of ex- 

 tinction, and those living in small, isolated habitats. Of the species in- 



100 



