AGE-RELATED DIFFERENTIAL TIMING OF SPRING MIGRATION WITHIN SEXES IN PASSERINES

Abstract

We examined differential timing of spring migration by age class for passerines banded at Long Point Bird Observatory from 1984 to 1998. Mean capture dates of after-second-year (ASY) males were earlier than second-year (SY) males for 19 of 20 species, 16 significantly so. Mean capture dates of ASY females were earlier than SY females for 11 of 12 species, 8 significantly so. There was no significant difference in the timing of migration between age classes for males of species with highly distinctive SY plumages and males of other species with more subtle plumage differences between age classes. For 12 species with adequate samples of both sexes, the mean difference in capture dates between age classes was significantly greater for males (3.5 days) than for females (2.1 days). These results suggest that differential migration by age class is widespread among passerines and that factors leading to the delayed arrival of young males also may affect females, though to a lesser extent.