THE INFLUENCE OF WEATHER, GEOGRAPHY, AND HABITAT ON MIGRATING RAPTORSON CAPE-MAY PENINSULA

For many shorebirds and passerines, stopovers in areas of concentrated resources increase survival during migration. For raptors, physical f actors have generally been considered to be the chief influence on mig ratory behavior, and few studies have collected quantitative data on t he use of resting and foraging habitat during migration. Our object wa s to survey three different habitats along a 30-km section of the Cape May peninsula. We measured abundance, flight altitude, and flight dir ection of eight species of migrating raptors to evaluate the influence of habitat and physical factors, including wind speed, wind direction , and location, on migratory behavior. Physical factors such as wind s peed and direction were weakly related to bird density and altitude, A lthough interactions among physical factors were significant, they wer e not consistent with predictions based on bird mass or wing-aspect ra tio. Habitat type was significantly associated with most species' alti tude and density. Birds generally occurred in higher densities and at lower altitudes above habitats similar to those used in breeding or wi ntering seasons. We suggest that the strong habitat association is due to the need for suitable foraging sites. Many migratory raptors are a ble to prey upon migratory birds, insects, and fish that also concentr ate at the end of the Cape May peninsula or in waters offshore. Most o f the raptors observed in Cane May are immature and inexperienced, and the concentration of similarly immature and inexperienced prey may pr ove to be a critical factor in successful migration along the Atlantic Coast.