Great Basin Naturalist


Portions of the Colorado, Dolores, Green, and San Rafael rivers in Utah were surveyed for the breeding Peregrine Falcon (Falco peregrinus anatum) from 1986 to 1988. Eleven physical variables were measured at nest cliffs (N = 22) and nonnest cliffs (N = 22) to discern descriptors of cliff choice and subsequent occupancy by breeding peregrines in unexplored habitat within the Colorado River and its tributaries. Ratio scale measurements were subjected to discriminant function analysis or the Mann-Whitney test to determine significant differences between cliff types. At nest cliffs, Rayleigh's and Kuiper's tests were applied to compass directions to ascertain mean direction and circular uniformity. None of the variables we selected revealed any appreciable descriptive ability, which suggests that certain physical attributes of a nest cliff are of questionable value in forecasting occupancy by breeding peregrines within that particular habitat.