Vancouver Avian Research Centre

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Warbling Vireo Vireo gilvus

Description:

A small gray-olive bird with white underparts sometimes slightly washed yellow, the Warbling Vireo is far less conspicuous to the eye than to the ear.
Since this bird is common, its song is part of our image of the spring and early summer-woods. It is best detected by its long flowing, warbling song which it sings throughout the day.
As in all vireos, the nostrils and part of the forehead are partly covered with bristlelike feathers; the bill is slightly hooked at tip with small notch.
Summer range of the Warbling Vireo is most of the United States, except the south eastern states and Alaska, and western Canada. The winter range is western Mexico and northern Central America.

Identification:

General: Medium sized stocky vireo with a relatively short bill, rounded head and subtle plumage. 14 cm long. 12g weight.

Adult Male: Upperparts primarily grayish-tinged olive green (except crown) and underparts whitish, often with pale yellowish tinge, especially on flanks and under tail-coverts. Face with moderately distinct white supercilium contrasting indistinctly with grayish eye-line, but otherwise very plain, without additional contrasting markings. Remaining plumage also plain, lacking distinct wing-bars or other contrasting markings or colours.

Adult female: Sexes are alike and plumages similar throughout the year.

Juvenile: Duller than adults overall, averaging more brownish, with very pale cinnamon or buffy wing-bars.

Similar Species: Warbling Vireo most is most frequently confused with Philadelphia Vireo, which occurs widely in eastern North America and Middle America. Both species are similar is size and general appearance. Other, larger, eye-lined vireos that might be confused with Warbling include Red-eyed Vireo which is larger and longer-billed and relatively shorter-tailed with distinct dark border above and below pale supercilium, creating a stronger facial pattern. The upperparts are olive greenish (not grayish).

Behavior: This is an inconspicuous bird. Gleans prey from tree foliage by both searching through and hovering above it.
Eats insects and some berries.
A tree-top bird, the male sings hour after hour, filling days with charming simple melody, matching summer calm of country from spring through hottest days of July and August.
Unlike the abrupt, broken, short phrases of other vireos, song is long, flowing warble.

Habitat: Throughout its range, this Vireo shows a strong association with mature mixed deciduous woodlands especially along streams, ponds, marshes, and lakes but sometimes in upland areas away from water. Also found in young deciduous stands that emerge after a clear-cut. Found at edges or openings (both natural and human-made) as well as forest interiors. Elevations of breeding habitats range from sea level to 3,200 meters.
Other habitats include urban parks and gardens, orchards, farm fencerows, deciduous patches in coniferous forests, mixed hardwood forests, and, rarely, pure coniferous forests.

Information:

Corresponding with its broad breeding distribution, this species occupies a variety of deciduous forest habitats and mixed coniferous, deciduous forest habitats, which are predominately riparian. It builds its nests in the forked limbs of trees from 1 to 40 meters above the ground at elevations ranging from sea level to over 3,000 meters. The species appears well adapted to human landscapes, as nests have been found in neighborhoods, urban parks, and orchards. The nest is a typical vireo suspended cup, woven around a forked branch. 3-5 dull white, heavily spotted eggs. As with all vireos, both parents share next-building and caring for the young.

Conservation Status:

Population trends for Warbling Vireo vary with geography. In California, for example, they have been declining steadily for the past 20 years, while long term trends in Ontario indicate that some populations are increasing. Commonly parasitized by the Brown-headed Cowbird.
 
Capture Rates


Capture rates (2010-2012; standardized as birds captured per 100 net hours) of Warbling Vireo indicate presence in the park from May through September, peaking in August and September as juveniles disperse. No captures from October to April reflect this migrant's movement to Mexico and Central America during the winter months.


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