The familiar North American breeding race (D. p. aestiva) of the Yellow Warbler, nests in deciduous thickets (frequently willow), often near wetlands. The breeding range of this abundant warbler extends from the Aleutian Is. east to Labrador, and in the south from California and Oklahoma to South Carolina [Lowther et al. 1999 (BNA)]. The main food is small invertebrates with some berries [Stevenson and Anderson 1994]. A single brood is reared in a nest built in the upright fork of a tree or shrub [Lowther et al. 1999 (BNA)]. The winter habitat is any non-montane forest edge, shrub or semi-open habitat, wetlands, or particularly mangrove swamps [Dunn and Garrett 1997]. The northeastern Yellow Warblers winter from central Mexico south through Central America to the Amazon River, mostly east of the Andes, although there is confusion with tropical resident races of this species [Lowther et al. 1999 (BNA)].
The migration is primarily nocturnal, although more often diurnal in the fall than most other warblers [Duncan and Weber 1985]. Migrants are found in virtually any semi-open area, departing Panama by the end of April [Wetmore et al. 1984]. They mostly fly around the Gulf of Mexico to Texas by April-May, then slowly north and east, with the northernmost birds reaching Churchill, Manitoba by early June. Fall migration is very early, many birds departing from the east by mid to late July, passing through Florida by mid-August to mid-October, and Costa Rica by September-October [Lowther et al. 1999 (BNA)].
Breeding Bird Survey data for North America (1966-1996) show no long-term trends, although southern New England populations are increasing at 1.3% per year [Sauer et al. 1997]. Yellow Warbler breeding success is lowered by cowbird parasitism, but some birds respond by recognizing cowbird eggs in their nests, relining the nest and re-laying. One warbler nest was relined to total six layers, covering 11 cowbird eggs [Berger 1955]. Historically, the clearing of forest may have led to population increases, but the draining and clearing of wetlands may have caused greater adverse effects [Lowther et al. 1999 (BNA)].
|
