Perching Birds

Wilson's Warbler  Wilsonia pusilla

Family: Wood Warblers, Parulidae

Audio: Martyn Stewart, © Naturesound.org

An estimated 54% of the species' North American population breeds within the Boreal Forest.

Description  4 1/2-5" (11-13 cm). Adult male olive green above and yellow below, with black crown patch. Most females and all young birds lack black crown and may be distinguished from other olive green warblers with yellow underparts by lack of wing bars, streaks, tail spots, or other markings.

Habitat  Moist thickets in woodlands and along streams; alder and willow thickets and bogs.

Nesting  4 or 5 brown-spotted white eggs in a bulky mass of leaves, rootlets, and moss, lined with hair and fine plant materials, concealed on the ground in a dense clump of weeds or sedge.

Voice  A rapid, staccato series of chips, which drop in pitch at the end.

Range  Breeds from Alaska eastward to Newfoundland and south to southern California, New Mexico, central Ontario, and Nova Scotia. Winters in tropics.

Discussion  It is easy to observe this common warbler, which has little fear of humans, because it searches the outsides of leafy branches, often catching flying insects on the wing like a flycatcher. During early summer, the foraging male utters long bursts of vivid song. It is named for Scottish-American ornithologist and artist Alexander Wilson (1766-1813).

Migration Info  Wilson's Warbler is represented in North America by three subspecies that probably have different migratory routes and schedules. The Pacific populations are the earliest migrants, arriving in British Columbia by the end of April. The other populations, which may cross any portion of the country from the Great Basin to the east coast, are relatively late migrants. The first arrivals are usually noted in the northern Great Lakes region in mid-May, but transients continue to pass through this area until mid-June. Recent studies indicate that the Pacific coast populations winter primarily in Baja California, Alaskan birds winter in the Honduras area, and the birds that winter in the central Mexican highlands come from several breeding sources. Wilson's Warblers are territorial in winter, and males and females are found in different habitats.