biologically significant impact has occurred, and it remains for society to deter- 

 mine if this change in black-billed magpie populations is acceptable or not. 



However, even with sound statistical documentation of a post-mining change 

 in one or more species or community parameters, the problem of establishing a 

 causal link between the observed change and the proposed facility remains. This 

 problem is seldom dealt with in the scientific literature, and no approach to 

 its solution has gained wide acceptability. It is felt that the number of con- 

 trols and number of replicates in this monitoring program should be sufficient 

 in establishing causalty with respect to localized mine-related impacts. Dif- 

 ficulty is anticipated, however, in linking observed biological changes to such 

 less localized changes as increased human population density, increased hunting 

 pressure, increased vehicular traffic, and plant emissions. 



199 



