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Baltimore Oriole
Icterus galbula
Order
PASSERIFORMES
– Family
ICTERIDAE
Authors: Rising, James D., and Nancy J. Flood

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Introduction

Adult male Baltimore Oriole, Iowa, May
Figure 1. Distribution of the Baltimore Oriole.

Historically a bird of woodland edge and open riparian woods, the Baltimore Oriole has adapted well to urban parks and suburban landscapes. This adaptability, as well as the bright orange and black coloration of the adult male, the clear, melodious song, and the characteristic, carefully woven pendent nest, make this oriole one of our most familiar songbirds. Males do not develop their bright coloration until their second Prebasic molt, in the fall of their second calendar year. Although yearling males (those in their first potential breeding season) resemble adult females, some successfully attract mates and raise young. The species is usually socially monogamous.

The Baltimore Oriole was illustrated and described by Mark Catesby in the first volume of his Natural History of Carolina, Florida and the Bahama Islands, published in 1731. Catesby named this bird the “Baltimore-Bird,” because black and orange were the colors of the Baltimores, the colonial proprietors of the Maryland colony. On the basis of Catesby’s description, Linnaeus named this species Coracias galbula (the small yellowish jackdaw) in the tenth edition of Systema Naturae, published in 1758. The English vernacular name “oriole” is based on the superficial resemblance of these birds to the orioles (Oriolidae) of the Old World.

Although a few Baltimore Orioles winter in the southern states, most migrate to the Neotropics. They start to leave their wintering grounds in February or March, and begin to arrive along the Gulf Coast in early April. Most individuals depart for their wintering grounds by mid-September. In winter and during migration, Baltimore Orioles are often seen in small groups composed of mixed ages and sexes.

In the Great Plains, this species frequently hybridizes with the Bullock’s Oriole (Icterus bullockii), despite marked differences between the 2 species in appearance, behavior, and vocalizations, and some difference in size. As a consequence of this hybridization, these two orioles were placed in a single species, the Northern Oriole (Icterus galbula), in the sixth edition of the American Ornithologists’ Union Check-list of North American Birds (1983), a decision widely reflected in the literature. Recently, the Check-list Committee separated these 2 orioles at the specific level (Monroe et al. 1995), and recent work indicates the 2 species may not be each other's closest relative (see Systematics).

Studies of the breeding biology of the Baltimore Oriole include Edinger 1985 (eastern Colorado), Flood 1984 (south-central Kansas), Labedz 1982 (central-western Kansas), and Pank 1974 (Massachusetts). The adaptive significance of the delayed plumage of males has been studied by Flood (1980, 1984, 1989), and molt by Sealy (1979), Rohwer and Johnson (1992), Rohwer and Manning (1990). Beletsky (1982a, 1982b) studied vocal behavior. Hybridization between Baltimore and Bullock’s orioles has been especially well studied, with the hybrid zone in the Great Plains being one of the best described in the literature (Rising 1996).