The Baltimore Oriole is the eastern counterpart of what was once considered a single species, the Northern Oriole. The Bullock’s Oriole is its western counterpart [AOU 1998]. Baltimore Orioles are highly adaptable; using a variety of woodland habitats in all seasons [Bent 1958]. They prefer open, deciduous woodlands to conifers and often nest in riparian areas [Rising and Flood 1998 (BNA)]. Insects compose the majority of their diet, but fruit and nectar are also important food sources, especially in winter [Timken 1970]. Baltimore Orioles breed in the U.S. east of the Rockies, although their range extends farther west in Canada. Their distribution is limited in the north to southern Canada and in the south to northern sections of Louisiana and Mississippi [Rising and Flood 1998 (BNA)]. This species is a complete migrant, with the vast majority of individuals wintering in Central America and northern South America, southern Mexico, the West Indies, and southern Florida (where they do not breed). Some individuals remain in other states over the winter, but only in small numbers [Rising and Flood 1998 (BNA)].
Migrants begin to leave their wintering grounds in February and March and arrive in Texas between mid-April and early May. Baltimore Orioles fly both overland along the coast of Mexico and across the Gulf of Mexico to reach the U.S. [Rising and Flood 1998 (BNA)]. The timing of this species’ arrival on the breeding grounds is typically quite predictable. Orioles begin arriving in Massachusetts in early May, with little annual variation [Bent 1958, Veit and Petersen 1993]. There is strong fidelity to breeding sites from year to year [Bent 1958, Rising and Flood 1998]. Migration is believed to be both nocturnal and diurnal, and migrants can often be found in small flocks of mixed ages and sexes [Rising and Flood 1998 (BNA)]. However, males typically arrive on the breeding grounds 2 – 3 days before females [Bent 1958].
Fall migration is relatively early, with orioles leaving their northernmost breeding areas in July and early August [Rising and Flood 1998 (BNA)]. In Massachusetts, adults have usually left by early August [Veit and Petersen 1993]. Migrants follow the Atlantic slope down the coast of Mexico, where they may arrive on their wintering grounds as early as late August [Rising and Flood 1998 (BNA)].
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