By evaluating an array of tracts it can readily be shown which are most and which 

 are least valuable as habitat for one or more species (Table 2). Rankings of this type 

 can provide input to decisions involving the sequence in which tracts will be dis- 

 turbed, and which tracts are preferred candidates for disturbance or protection. Such 

 rankings can also be used to project the cumulative impacts of a number of separate 

 disturbances on a particular species. 



Finally, PATREC can be used for habitat classification or inventory. Applied over 

 a large area (large being relative to the life cycle requirements of the animal for which 

 the habitat is being classified), the probability values (0.01-0.99) for the potential 

 population density to be high can be divided into increments (e.g., of 10) and plotted 

 on a map to represent areas of different habitat quality. 



PATREC can be applied quickly and inexpensively and can provide predictions as 

 accurate as current knowledge permits or as circumstances warrant. The logic of the 



Table 2. Ranking of 1 4 oil shale tracts in Colorado and Utah by 

 mountain bluebird nesting habitat quality according to 

 PATREC results, September, 1979.1 



Tract 



P(H) 



P(L) 



Estimated 



potential density Estimated potential 



on tract population size 



(bluebirds/mi^) on tract* 



'Should be interpreted as follows: The estimated potential population size 

 according to the acreage figures, PATREC nnodels and environnnental 

 nneasurement data used. Each of those conditions constitutes a possible 

 source of error in the resulting estimates. 



176 



