COMPARISON OF SPRING AND FALL MIGRATION OF AMERICAN REDSTARTS ON APPLEDORE ISLAND, MAINE

Abstract

On Appledore Island, Maine, American Redstarts (Setophaga ruticilla) were encountered frequently during both spring and fall migration from 1990 to 1999. Males arrived earlier than females during spring, but arrival dates of males and females did not differ significantly during fall. Also, adults arrived earlier than young birds during spring, but not during fall. Recapture of banded birds at least one day after initial capture occurred more frequently during fall than spring, although mean stopover length did not differ significantly between the two seasons. Although recaptured individuals increased in mass during stopover during both seasons, mass increases were significant only during fall. However, rates of mass increase estimated by regression of condition over time of capture indicated greater mass increases during spring. Neither recapture rates, stopover lengths, nor mass changes differed significantly between males and females or between age groups within either season. These results indicate that although many American Redstarts were encountered on Appledore Island during both spring and fall migration, birds were using the site differently during the two seasons. Spring migration was more concentrated with few observed stopovers, while fall migration was protracted with increased rates of recapture. American Redstarts may have been responding differently to this site during spring and fall migration because of the proximity to breeding grounds and distance from winter grounds as well as the location of the Atlantic Ocean, which represents an ecological barrier during fall migration.