Productivity of Peregrine Falcons (Falco Peregrinus) in the Greater Yellowstone Area, 1988-1990

Publication Date


Type of Culminating Activity


Degree Title

Master of Science in Raptor Biology



Major Advisor

William Burnham


As of 1980, there were no known breeding pairs of peregrine falcons (Falco peregrinus anatum) in the tri-state region of Idaho, Wyoming, and Montana, known collectively as the Greater Yellowstone Area (GYA). Efforts were begun to re-establish a population through the release of captively-produced young. By 1990, approximately 505 young peregrines had been released at 30 different sites within the GYA.

Area wide, cooperative survey and monitoring programs were undertaken from 1988 through 1990. Twenty-five newly-occupied territories were identified. Fifty-seven nesting attempts were monitored. Productivity averaged 1.3 young per breeding attempt and 2.5 young per successful pair.

Nesting phenologies were determined through repeated nest visits. Mean fledging date was 16 July. Band status was identified for breeding adults and used to estimate turnover rates. Adult turnover was estimated at 12% for both sexes combined. Eggshell fragments, and unhatched eggs were collected, measured and analyzed. Mean eggshell thickness averaged 0.317 mm, 12% thinner than the pre-1947 mean of 0.359 mm. These results are similar to those reported from other studies of recovering peregrine populations in the Rocky Mountain region.

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