create density index isopleths that show general patterns of distribution 

 (Figures 11 and 12). As indicated on these figures, pronghorn are most commonly 

 found in the southwestern, south-central, and northwestern portions of the Mine 

 Study Area in summer. During the mild winter of 1980-1981, pronghorn were very 

 abundant on the rolling grassland and sagebrush areas immediately southwest of 

 the Mine Study Area. 



BIRD COM.MUNITY PARAMETERS 



Waterfow'l Communities 



The drought conditions present during the spring and summer of 1980 had a 

 marked effect on waterfowl production; waterfowl productivity showed a drastic 

 decline over 1979. 



Breeding season species composition of all waterfowl and other large water 

 birds observed in the Mine Study Area is presented in Table 10. Year-to-year 

 changes in waterfowl species composition are portrayed graphically in Figure 13. 

 Species composition was remarkably similar to that noted in 1979, with the 

 mallard again being the predominant breeding waterfowl species. 



Waterfowl breeding season census data for stockponds in the study area are 

 summarized in Table 11. These data are converted to production and density 

 estimates in Table 12; production is shown graphically in Figure 14. At the 

 beginning of the 1980 breeding season, most of the larger stockponds were nearly 

 filled and use by waterfowl was relatively high. In fact, a census estimate of 

 the number of pairs using the Mine Study Area in 1980 indicated a substantial 

 increase in waterfowl use from 1979 (Table 12). However, stockponds dried out 

 rapidly over the summer and 1980 production actually showed a marked decline 

 over 1979 (Table 12, Figure 14), dropping to approximately the level of 1977, a 

 year of severe drought. The decrease in waterfowl use over the summer is shown 

 on Figure 13. This can be compared to the increase observed during the summer 

 of 1979 (DNRC 1980). Such a sharp decrease in waterfowl production is believed 

 to be due to a decline in residual grass cover, as well as reduced water levels 

 in the stockponds . 



Waterfowl data obtained during the roadside surveys indicated a similar 

 trend. As shown in Figure 15, both the number of species and number of 

 observations of Anatidae and other water birds (as recorded on June surveys of 

 five observation routes) showed a decline between 1979 and 1980. 



Data on broods observed during 1980 are presented in Table 13. 



Roadside Wildlife Survey 



Data obtained during the 15 roadside surveys conducted in 1980 are presented 

 in Appendix C. The cumulative numbers of species observed during all May-July 

 runs (1977-1980) are presented in Table 14. 



Table 15 summarizes 1979-1980 changes in May-July sample abundances of 

 selected species, based on data obtained during runs of five roadside survey 

 routes. Figure 3, which shows year-to-year changes in sample abundances of 

 ring-necked pheasants, exhibits the type of graphs that were prepared to monitor 

 individual species. 



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