INTERFERENCE ASYMMETRIES AMONG AGE-SEX CLASSES OF RUFOUS HUMMINGBIRDSDURING MIGRATORY STOPOVERS

Three age-sex classes of rufous hummingbirds (Selasphorus rufus) overl ap temporally and defend feeding territories during migratory stopover s in the Sierra Nevada of California. We demonstrate that these classe s differ in their ability to secure and maintain high-quality feeding territories for refueling, and that these differences result in differ ences in resource use. Data on acquisition of territories, territory c haracteristics, and responses of territory owners to intruders suggest that several mechanisms are involved in determining dominance, involv ing sex- and age-related differences in wing disc loading, coloration, and experience. We discuss the implications of these results for unde rstanding intraspecific variation in migration strategies.