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Editor’s Note: Genetic data indicate that P. noveboracensis and P. motacilla, formerly placed in the genus Seiurus, are not closely related to and do not form a monophyletic group with the type species of the genus, S. aurocapilla. See the 51st Supplement to the American Ornithologists’ Union Checklist of North American Birds for details. Future revisions of this account will reflect this change.
The Northern Waterthrush is a bird of the northern forests, adding its loud, ringing song to the wooded swamps, bogs, and banks of North America’s great rivers and lake shores. Most North American birdwatchers see it only on migration in back yards, city parks, and wet places, as it migrates to and from its wintering grounds in the tropical mangroves of Central and South America.
This is a large wood warbler, not a thrush, rarely seen far from water. Like its close relative the Louisiana Waterthrush (Seiurus motacilla), it continually bobs its body and wags its tail—a key to identification. It is smaller in body and bill than the Louisiana Waterthrush, with subtle differences in plumage, leg color, and song. Nevertheless, some data on Northern and Louisiana waterthrushes must be questioned because the two species were confused. Alexander Wilson, for example, and others of his time, failed to recognize them as distinct species.
In the northeastern United States, where the Northern and Louisiana waterthrushes often overlap in range and habitat, the Northern Waterthrush behaves aggressively toward other conspecifics but not toward the Louisiana. These two species have evolved differences in foraging and other behaviors which help to separate them; no hybrids are known between them.
Across Canada and Alaska, the stronghold of the Northern Waterthrush, its habitat appears fairly secure, at least compared with that of many other warblers. On its main wintering range, by contrast, its habitat is increasingly threatened. Mangrove (Rhizophora sp.) forests of the West Indies, Mexico, Central America, and northern South America are being cut as burgeoning human populations demand fuel, food, and space.