Birds: Baltimore Oriole Reclassified as Separate Species

June 96

The Baltimore oriole has recently been reclassified as a separate species after more than 20 years of being lumped together with the Bullock's oriole, a closely related species. The reclassification was announced in the 40th supplement to the American Ornithologist's Union (AOU) Check-list of North American Birds, the official register of avian names in the United States.

The Baltimore oriole, scientifically known as Icterus galbula, earned its name from the males' flashy black-and-orange plumage reminiscent of the heraldic colors of Lord Baltimore, the English noble credited with founding the state of Maryland. The name held firmly for more than 200 years until scientists observed that the species was crossbreeding with another bird, the Bullock's oriole, in the Great Plains. When such crossbreeding produces fertile young, biologists regard the hybridization as a sign that two seemingly different birds are in fact members of the same species. So, to the disappointment of many birdwatchers, in 1973 the AOU officially lumped the two birds into a single species-the northern oriole.

Since 1886 the AOU, through its classification and nomenclature committee, has been regulating avian names in North America. The seven-member committee is composed of avian taxonomists, scientists who study bird classifications. The committee convenes twice a year to consider changes to the Check-list proposed by scientists and birdwatchers alike. Its aim is to ensure that every bird is accurately classified from Canada to Hawaii to Central America and the Caribbean. In pursuit of that mission, the nomenclature committee over the years has produced six editions of the Check-list, most of which have announced extensive changes both in common and scientific bird names. Today the Check-list features nearly 2000 birds.

Some names are changed simply to bring them in line with related European species. For example, in the 40th supplement, the Northern Hobby became the Eurasian Hobby, the name by which it is known in Great Britain. Anyone can suggest name changes, but most recommendations are based on published scientific data indicating that a bird has been misclassified. Taxonomic considerations, such as differences in coloring, vocalization, geographic distribution, migratory patterns, and skeletal characteristics, can result in a name change or reclassification. For example, the recent Check-list reclassifies as a separate species the Bicknell's thrush, which was formerly lumped with the Gray-Cheeked thrush. The change was based on differences in vocalization, habitat preferences, and migration patterns. The 40th supplement adds 25 new listings to the Check-list, 19 of which are due to the splitting of species.

Taxonomic considerations were what prompted the decision to list the Baltimore oriole and the Bullock's oriole as separate species. Recent field studies suggested that very little breeding had actually occurred between the two species, even though the Baltimore oriole has been spreading westward and increasingly overlapping the range of the Bullock's oriole in the Great Plains. In the hybridization zone, scientists found few examples of hybrid offspring.

In recent years, genetic testing has added another dimension to nomenclature considerations. Several scientific name changes in the recent Check-list were based on analysis of deoxyribonucleic acid (DNA), the material in a cell that carries the genetic code across generations. For example, DNA evidence showed that the great egret, a type of heron, is more closely related genetically to a different genus, resulting in its scientific name being changed from Casmerodius albus to Ardea alba.

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"Birds: Baltimore Oriole Reclassified as Separate Species ," Microsoft(R) Encarta(R) 96 Encyclopedia. (c) 1993-1995 Microsoft Corporation.

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