Mitchell et al. (2010) reported that juvenile Blackpoll Warblers (Dendroica striata) raised in northwestern Newfoundland moved generally toward the southeast during the post-fledging period. They concluded (p. 651) that this finding failed to support their prediction from the migratory-commencement hypothesis. Their basis for this prediction (p. 645) was as follows: “We predicted that if meso movements represent initial migratory displacements, these moves should be oriented to the southwest at each study site, parallel to the known axis of migration (Richardson 1972).”

The article by Richardson (1972) summarized his radar studies of migration over Nova Scotia and New Brunswick, covering an area that extended east of Cape Breton Island (to 58° W), almost as far east as the longitude of the study area of Mitchell et al. (49° 47′ N, 57° 16′ W) in Newfoundland. Richardson did not report a single “axis of migration.” His summary statement was the following: “In addition to the dense SW movements and the less dense reverse flights, movements to the SE and [word omitted] were also very common. Both passerines and shorebirds were commonly involved.” The remainder of the article indicated that the word omitted from this passage was either S or SSE. Richardson did not identify the passerines involved in the SE movements in his 1972 article, but, from a variety of other lines of evidence, he identified them as primarily Blackpoll Warblers in several subsequent papers in major ornithological journals (Richardson 1976, 1978, 1980),. The transoceanic migration of the Blackpoll Warbler, in which it departs SE or SSE from southeastern Canada and the northeastern USA, crosses the western North Atlantic Ocean and makes landfalls in the West Indies and South America, has been abundantly documented in other literature. It was referred to in the most recent monograph on the species (Hunt and Eliason 1999), the most recent reviews of its migration (Nisbet et al. 1995, Baird 1999), and the most recent book on the migration ecology of birds (Newton 2007). Additional supporting evidence has been supplied by recent field studies in the Caribbean (Latta and Brown 1999, McNair et al. 2002a,b).

The distance from southern Newfoundland over the western North Atlantic Ocean to northern South America is only about 200 km longer than that from Sydney, Nova Scotia, so a nonstop flight from Newfoundland is well within the capabilities of the Blackpoll Warbler. We do not have a strong hypothesis about the species' direction of migration from Newfoundland (Nisbet 1970), but Richardson (1972, 1980) stated that he observed SE/SSE departures of passerines at his easternmost radar station (Sydney, Nova Scotia), although the densities were not as high as those at the stations in New Brunswick and central Nova Scotia where Blackpoll Warblers are numerous during autumn migration (also coastal southwestern Nova Scotia; Davis 2001, Crewe et al. 2008, Bird Studies Canada 2011). Many Blackpoll Warblers raised in northwest Newfoundland might initially migrate southwest to Nova Scotia, New Brunswick, or New England before heading southeast on transoceanic migration, but the findings of Mitchell et al. (2010) that juvenile Blackpoll Warblers move southeast from northwestern Newfoundland during the post-fledging period are fully consistent with the migratory-commencement hypothesis. Indeed, they provide new evidence that Blackpoll Warblers move toward their ultimate destination in the post-fledging period, regardless of the actual route they take subsequently to get there. The post-fledging period of Mitchell et al. (2010) extended into late August (to 26 August), when Blackpoll Warblers initiate migration in the Maritime Provinces (Nisbet 1970). We suggest that Mitchell et al. (2010) reinterpret their data in the context of the Blackpoll's known orientation to the southeast during autumn migration and reconsider the migratory-commencement hypothesis, which we believe they have inappropriately rejected.

We appreciate the efforts of A. E. Heagy of Bird Studies Canada, D. J. T. Hussell, and L. Laurin of the Canadian Bird Banding Office for providing information in response to our queries. We also appreciate comments received from D. J. T. Hussell, I. A. McLaren, G. W. Mitchell, and one anonymous individual on a draft of this commentary.