The Canada Warbler has one of the longest migrations of the eastern warblers and spends little time on its breeding grounds [Conway 1999 (BNA)]. It breeds in Canada from eastern British Columbia to the Maritime Provinces, and south to the northeastern U.S. and high elevations of the Allegheny Mountains [Conway 1999 (BNA)]. The principal wintering areas are in northern South America: Columbia, Peru, and Ecuador [Paynter 1995]. Canada Warblers inhabit cool, moist forests with dense understories and moist groundcover [Dunn and Garrett 1997]. They often nest in swampy areas or near open water, in a wide variety of deciduous and coniferous forests [Conway 1999 (BNA)]. Canada Warblers have a late spring migration and an early fall migration compared with other warblers [Conway 1999 (BNA)]. Furthermore, the migrations are fairly rapid [Conway 1999 (BNA)]. In spring, these warblers migrate north through the mountains of Central America and Mexico, along the coast of Texas, and northward through the eastern states [Conway 1999 (BNA)]. They are not believed to be trans-Gulf migrants [Cramp and Perrins 1994] despite early reports to the contrary [Bent 1953]. The spring route includes a broad front from the Ohio valley, east to the Atlantic coast and it is believed that migration through the U.S. occurs over a period of 3 – 4 weeks [Bent 1953]. Canada Warblers depart their wintering grounds between late March and mid-April (depending upon location) and arrive in southern Texas in early to mid-May [Conway 1999 (BNA)]. From there, they migrate to New England relatively quickly, arriving in Massachusetts in mid- to late May [Veit and Petersen 1993]. They reach their northernmost breeding areas in western Canada in late May to early June [Conway 1999 (BNA)]. In spring, males arrive on their breeding grounds slightly in advance of females [Conway 1999 (BNA)]. Some evidence suggests that adult males may arrive before second-year males [Francis and Cooke 1986]. The fall migratory route is much the same as that in the spring, but possibly further west [Conway 1999 (BNA)]. These nocturnal migrants do not show any differential migration of sexes in the fall, but immatures generally migrate earlier than adults [Leberman and Clench 1971]. Canada Warblers have been observed in mixed-species flocks in the fall, primarily composed of other warbler species [Conway 1999 (BNA)]. They often occur in association with Wilson’s Warblers (Wilsonia pusilla) [Dunn and Garrett 1997]. While migrating, they prefer shrubbier, more open habitat than they do during the breeding season [Dunn and Garrett 1997], and may even be found in urban areas [Conway 1999 (BNA)].
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Observations
The comparatively low sample size of 139 Canada Warblers militates against the detection of significant habitat differences between states. Habitat differences were not significant. For example, the peak number in VT B sites was mostly driven by one flock of 6 birds in one transect.
Apart from a very few early arrivals in period 3, Canada Warblers were only detected in periods 4 and 5 (late May-early June). There was no clear drop in numbers by period 5, so many of the migrants may have stayed to breed. On the other hand, our transects avoided the typical breeding habitat of shrubby wetlands, being chosen for upland deciduous forest habitat. |
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