Baltimore Oriole Icterus galbula Scientific name definitions

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 some Baltimore Orioles overwinter in the southern states, most migrate to the Neotropics and overwinter primarily in Central America and northern South America. They start to leave their overwintering grounds in February or March, and begin to arrive along the Gulf Coast in early April. Most individuals depart for their overwintering grounds by mid-September. During overwintering and migratory periods, 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 two 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 (1 American Ornithologists' Union (1983) Check-list of North American Birds. Sixth edition. American Ornithologists' Union, Washington, DC, USA. Close ), a decision widely reflected in the literature. The two orioles were reclassified as separate species in 1995 (2 American Ornithologists' Union (1995). Fortieth supplement to the American Ornithologists' Union Check-list of North American Birds. Auk 112:819–830. Close ), and research indicates the two species are not each other's closest relative (see Systematics).

Studies of the breeding biology of the Baltimore Oriole include Edinger (3 Edinger, B. B. (1985). Limited hybridization and behavioral differences among sympatric Baltimore and Bullock's orioles. M.S. thesis, University of Minnesota, Minneapolis, MN, USA. Close ; eastern Colorado), Flood (4 Flood, N. J. (1984). Adaptive significance of delayed plumage maturation in male Northern Orioles. Evolution 38:267–279. Close ; south-central Kansas), Labedz (5 Labedz, T. E. (1982). A comparison of the reproductive efficiency of second year and after-second-year male Northern Orioles (Icterus galbula) near Hays, Ellis County, Kansas. M.S. thesis, Fort Hays State University, Hays, KS, USA. Close ; central-western Kansas), and Pank (6 Pank, L. F. (1974). Nesting biology of the Baltimore Oriole. M.S. thesis, University of Massachusetts, Amherst, MA, USA. Close ; Massachusetts). The adaptive significance of the delayed plumage of males has been studied by Flood (7 Flood, N. J. (1980). The adaptive significance of delayed plumage maturation in the Northern Oriole. M.S. thesis, University of Toronto, Toronto, ON, Canada. Close , 4 Flood, N. J. (1984). Adaptive significance of delayed plumage maturation in male Northern Orioles. Evolution 38:267–279. Close , 8 Flood, N. J. (1989). Coloration in New World orioles. 1. Tests of predation-related hypotheses. Behavioral Ecology and Sociobiology 25:49–56. Close ), and molt by Sealy (9 Sealy, S. G. (1979). Prebasic molt of the Northern Oriole. Canadian Journal of Zoology 57:1473-1478. Close ), Rohwer and Johnson (10 Rohwer, S., and M. S. Johnson (1992). Scheduling differences of molt and migration for Baltimore and Bullock's orioles persist in a common environment. Condor 94:992-994. Close ), and Rohwer and Manning (11 Rohwer, S. and J. Manning (1990). Differences in timing and number of molts for Baltimore and Bullock's orioles: Implications to hybrid fitness and theories of delayed plumage maturation. Condor 92:125-140. Close ). Beletsky (12 Beletsky, L. D. (1982). Vocal behavior of the Northern Oriole. Wilson Bulletin 94:372-380. Close , 13 Beletsky, L. D. (1982). Vocalizations of female Northern Orioles. Condor 84:445-446. Close ) 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 (14 Rising, J. D. (1996). The stability of the oriole hybrid zone in western Kansas. Condor 98:658-663. Close ).