Recent studies have suggested climate change could amplify the differences between arrival dates of male and female passerines. We investigated the generality of this finding and additional questions related to protandry by analyzing 32 years of banding data for seven species of migratory passerines. Six species exhibited significant protandry with males arriving on average between 2 and 6 days earlier than females. Only Baltimore Orioles (Icterus galbula) did not have significant differences between average arrival dates of males and females. The magnitude of protandry did not change in response to warming spring temperatures during the period of study, and none of the ecological variables examined explained variation in the amount of protandry. Males of all species studied were significantly larger than females. However, the magnitude of size difference also did not explain the amount of protandry observed. Arrival dates of males and females within each species tended to follow similar trends over time and sex ratios did not change over time for any species. Changes in sex ratios of Mourning Warblers (Geothlypis philadelphia)–more females in warmer years—however, were significantly related to mean temperature in the year of migration. Protandry may remain fairly consistent as the climate changes, although further research is needed to test the generality of this pattern.
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Vol. 124 • No. 2