National Geographic Magazine/Volume 31/Number 4/Friends of Our Forests/Wilson's Warbler
The Warblers of North America
Wilson's Warbler (Wilsonia pusilla pusilla)
Range: Breeds in Boreal Zones from tree limit in northwestern and central Mackenzie, central Keewatin, central Ungava, and Newfoundland south to southern Saskatchewan, northern Minnesota, central Ontario, New Hampshire, Maine, and Nova Scotia; winters in eastern Central America from Guatemala to Costa Rica.
This tiny warbler ventures farther north than many bigger and apparently, hardier species, and Nelson found it in Alaska “one of the commonest of the bush-frequenting species, … extending its breeding range to the shores of the Arctic Ocean wherever it finds shelter.” Cooke also found it in Colorado breeding from 6,000 to 12,000 feet elevation.
The black-cap is a nervous, energetic, little fellow, now essaying the rôle of flycatcher, now hunting for insects among the foliage, while ever and anon it jerks its tail up and down as though constant motion were the chief end of existence. It has a short, bubbling, warbling song which has been likened to the songs of several other species, but which possesses a tone and quality all the bird's own. Its nest is built on the ground, is composed chiefly of grasses, and the eggs do not differ in essential respects from those of other warblers.
It is noteworthy that the West Coast form of the black-cap chryseola breeds as far south as Los Angeles, and that its nest instead of being built on the ground is placed in the crotch of a limb or in a bunch of weeds or nettles.