Movements of Juvenile Blackpoll Warblers Prior to Autumn Migration in Newfoundland Reconsidered

In their commentary, McNair and Nisbet (2011) suggest that we (Mitchell et al. 2010) may have incorrectly rejected the migration-commencement hypothesis as a possible explanation for the broad-scale southeasterly movements made by juvenile Blackpoll Warblers (Dendroica striata) in northwestern Newfoundland during the post-fledging period. They argue that because the dominant orientation of Blackpolls departing Nova Scotia, New Brunswick, and the northeastern U.S. for transoceanic migration to the Caribbean and South America is to the south-southeast (reviewed by Nisbet et al. 1995), the pattern of movement reported in Mitchell et al. (2010) is actually consistent with the migratorycommencement hypothesis. For our paper (Mitchell et al. 2010), we defined initial migratory movements as broad-scale movements away from the natal area, and made the a priori prediction that these movements should be parallel to the “known” axis of migration. Although we did not state so explicitly, we interpreted axis of migration as reflecting the immediate migratory trajectory of birds leaving the island of Newfoundland rather than the eventual migratory trajectory from the southwest shore of Nova Scotia or the Gulf of Maine. Our prediction that initial migratory movements should be to the southwest was based on Richardson’s (1972:11) radar observations of songbirds migrating from Newfoundland to Nova Scotia (a southwest trajectory). Indeed, McNair and Nisbet (2011) agree that many juvenile Blackpolls raised in