"harassment has a significant impact on individuals and the 

 population: 1) it may result in death through predation, acci- 

 dents and increased hunting mortality, 2) it may affect growth 

 and development of individuals, 3) it may cause abandonment of 

 some ranges or parts of them, and 4) it alters activity pat- 

 terns and distribution on occupied areas." 



A shift in lambing and nursery areas from the historical areas 

 dDserved by Brink (1941) to those occupied after the completion of 

 the project (Brown 1979) was probably directly related to increased 

 human activity and loss of spring habitat. This shift has caused 

 the sheep to use an area of lower nutritional value (an area of 

 later "green-up") as a parturition area, and has probably been a 

 contributing factor in the decrease in the sheep population on the 

 Ural-Tweed range. In addition, the lengthy sections of shear high- 

 walls (up :o 0.6 miles) created when the h: ghway was constructed, 

 act as a barrier to movement to the habitats between the highway and 

 the reservoir. 



5) Estimated Losses Due to the Project 



- Quantitative loss estimate: 



- An estimated loss of 4,350 acres of crucial winter and 

 spring range. 



- An estimated loss of 78 to 102 bighorn sheep as a result 

 of the Libby Dam project. 



- Qualitative loss estimate - high. 



6) Derivation of Loss Estimate 



A figure illustrating the estimated minimum population levels 

 of the Ural-Tweed bighorn sheep herd from 1934 to date was prepared 

 (Figure 2). This figure illustrates the catastrophic population 

 decline that occurred in the late 1960's and early 1970's, with the 

 population stabilizing at approximately 25 animals (Line A). Declines 

 such as this have occurred naturally in numerous bighorn sheep 

 populations. The decline experienced by the Ural-Tweed population 

 closely parallelled those described by Stelfox (1976) for five 

 bighorn sheep populations in Canada's National Parks, where over- 

 grazing and reduced physical condition, resulting in pneumonia- 

 lungworm disease, combined to cause a rapid mortality of at least 75 

 percent of the population. The decline of the Tarryall population 

 in Colorado was even more dramatic, with cin over-winter (1923-24) 

 decline from an estimated 350 bighorn sheep to 12 head, a 96.5 

 percent decrease (Buechner 1960). The decline of Ural-Tweed popu- 

 lation may have been a natural phenomenon-pneumonia-lungworm disease 

 - occurring with or without the construction activity and resultant 

 loss of habitat, or it may have directly resulted from the construc- 

 tion of the Libby Dam project ajid corresponding increase in human 

 activity and harassment. 



35 



