Long-term prairie falcon population changes in relation to prey abundance,weather, land uses, and habitat conditions

We studied a nesting population of Prairie Falcons (Falco mexicanus) in the Snake River Birds of Prey National Conservation Area (NCA) from 1974-1997 to identify factors that influence abundance and reproduction. Our sampling period included two major droughts and associated crashes in Townsend's gr ound squirrel (Spermophilus townsendii) populations. The number of Prairie Falcon pairs found on long-term survey segments declined significantly from 1976-1997. Early declines were most severe at the eastern end of the NCA, where fires and agriculture have changed native shrubsteppe habitat. More r ecent declines occurred in the portion of canyon near the Orchard Training Area (OTA), where the Idaho Army National Guard conducts artillery firing a nd tank maneuvers. Overall Prairie Falcon reproductive rates were tied clos ely to annual indexes of ground squirrel abundance. but precipitation befor e and during the breeding season was related inversely to some measures of reproduction. Most reproductive parameters showed no significant Vends over lime, but during the 1990s, nesting success and productivity were lower in the stretch of canyon near the OTA than in adjacent areas. Extensive shrub loss, by itself, did not explain the pattern of declines in abundance and reproduction that we observed. Recent military training activities likely h ave interacted with fire and livestock grazing to create less than favorabl e foraging opportunities for Prairie Falcons in a large part of the NCA. To maintain Prairie Falcon populations in the NCA, managers should suppress w ildfires, restore native plant communities. and regulate potentially incomp atible land uses.