Brigham Young University Science Bulletin, Biological Series


This study was undertaken to record the known history of the Peregrine Falcon (Falco peregrinus) in Utah as we have been able to construct it from both the literature and from our original research that extends over about a 30-year period in the state. The present total population of the peregrine in Utah is possibly only 10 percent of what it has been in historic times. In an effort to find explanations for the decline, we have explored hypotheses of climatic changes, impact of pesticides, disease, and human disturbances. We conclude that pesticide contamination and climatic changes may have been the major reasons for their decline in Utah.

A general background of the geographical and ecological distribution of the species in Utah is provided as are also details of its nesting behavior from some Wasatch Mountain eyries. Our data suggest that its nesting density along the Wasatch Mountains was about the same order of magnitude as nesting densities in other regions of North America that are generally considered more favorable to the peregrine.

We have considered some of the environmental factors that may limit the species in Utah and especially its relationship with a congener, the Prairie Falcon (Falco mexicanus). We conclude that the peregrine may live jointly with the Prairie Falcon with a minimum of intraspecific competition. We present evidence which suggests that the peregrine has been in Utah since the late Pleistocene and that it has had a long history of sympatric existence with the Prairie Falcon.