The Black-throated Green Warbler is a common migrant and breeder throughout the northeastern U.S. Its range extends in the north from the maritime provinces of Canada through central and southern Canada [Morse 1993 (BNA)]. It breeds in the Great Lakes region and south to Alabama, where it is restricted to upper elevations in the Appalachians [Morse 1993 (BNA)]. This insectivore can be found in a wide variety of woodland habitats, often preferring the complex vegetative structure present in second growth or woodland edges [Dunn and Garrett 1997]. The Black-throated Green Warbler is typically associated with conifers, although it breeds in deciduous forests in the southern Appalachians [Morse 1993 (BNA)]. In addition, the geographically distinct D. v. waynei subspecies inhabits cypress swamp forests in the Carolinas and Virginia [Morse 1993 (BNA)]. Black-throated Greens winter primarily in Mexico and Central America [Morse 1993 (BNA)], with a small population in the West Indies, particularly Cuba, that is believed to be D. v. waynei [AOU 1957].
In spring, migrants appear to use both a trans-Gulf and a land route, and proceed northward east of the Great Plains [Dunn and Garrett 1997]. This species is rare in the spring on the southeastern coastal plain and more numerous inland [Dunn and Garrett 1997]. Migrants appear in the southern U.S. in March, and may arrive in Massachusetts in late April [Bent 1953]. However the peak of migration through Massachusetts is in the first half of May [Veit and Petersen 1993]. Migration, as in many warblers, is nocturnal [Morse 1993 (BNA)], and males typically arrive on their breeding grounds before females [Bent 1953].
The route used by migrants in the fall is the reverse of that used in the spring [Bent 1953]. In the fall, however, there is a slight eastward shift of the broad front used in the spring, with more birds migrating along the Atlantic coast before crossing the Gulf of Mexico [Dunn and Garrett 1997]. Migrants depart their northern breeding grounds in late August and their more southern breeding grounds through October [Bent 1953]. In Massachusetts [Veit and Petersen 1993] and New Hampshire [Delorey 1996], most migration occurs through September. Black-throated Green Warblers often form mixed-species flocks in the fall, associating with chickadees, titmice, and other warblers [Morse 1993 (BNA)].
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Observations
This coniferous breeding warbler was migrating through primarily deciduous forest in our study area. Some birds were detected in A and B sites, along the Connecticut R. and its main tributaries, but most abundantly in C sites in all states. MA recorded the highest density in all three sites. Only the exceptionally early migrants were recorded in period 1, while the three southern states showed peaks in periods 3 and 4. The northernmost sites in VT peaked in period 4. By period 5, numbers had dropped as migrants departed northwards; there were fewest breeders in CT.
On many transects, mean numbers were influenced by occasional larger flocks of this normally rather evenly dispersed migrant species. |
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