Impacts of Regional Cold Front and Localized Weather Phenomena on Autumn Migration of Raptors and Landbirds in Southwest Idaho
Dr. James Belthoff
Weather has a significant effect on avian migration but determining if the effect is similar across diverse geographic regions and across all species remains to be determined. We evaluated the impact of regional cold fronts and localized weather phenomena on the autumn migratory timing of multiple landbirds and raptor species in southwest Idaho. The focus of the analysis was on the total landbirds and the top ten individual landbird species by volume along with total raptors and the top eight individual raptor species. Using 13 years of data from the Idaho Bird Observatory in southwest Idaho (1997-2009), including standardized landbird mist-net captures and raptor counts during autumn migration, we determined significant patterns which differ from the established literature with regards to the effect of regional cold fronts on fall migration. Our data show a depression of migratory volumes of most species on the days immediately before, during, and after the passage of a cold front, with peak flights for most species occurring many days later. Wind speed had the broadest impact of ten weather related variables. Lastly, we present hypotheses that could explain the unique impact of weather phenomena on avian migration in the western United States, most notably that most avian species choose to migrate during calm winds, high pressure, and between cold fronts when the opportunity presents itself.