Bird of the Week: Yellow-rumped Warbler

Few warblers deign to spend the winter months in North America, preferring the warm climates and easy meals of the tropics. The Yellow-rumped Warbler is a notable exception, found in great numbers across the southern and eastern United States each winter and as far north as Newfoundland. The warbler’s success is attributable in large part to its diet, transitioning easily from protein-rich insects to comparatively less nutritious berries in lean times. In the northern part of their winter range, these birds are sustained by the berries of the bayberry or wax myrtle. The waxy coating of myrtle berries is high in fat and energy, but is indigestible to most birds. The Yellow-rumped Warbler is uniquely able to digest these berries, allowing it to survive in climates that would send other warblers packing for Guatemala. Of interest to taxonomically-inclined birders is the fact that this warbler was once two– and may yet become four! Until about forty years ago, the bird now known as the Yellow-rumped Warbler was recognized as two separate species, the “Audubon’s” and “Myrtle” warblers. The two were merged in 1973, but recent studies suggest that genetic differences among populations warrant the species being split into as many as four new species– adding three new entries to the meticulous birder’s life list.

Compiled by Owen Moorhead. Sources include the Cornell Lab of Ornithology and National Audubon Society.
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