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 summerwoods. It is a long, flowing, warbling song, which it sings throughout the day. Its breeding range extends east to west through the center of North America. The winter range extends from western Mexico to northern Central America.
Adult Male (spring/summer)
Head is olive gray with pale lores and weak pale white supercilium. Face is plain. The nostrils and part of the forehead are partly covered with bristle-like feathers. Back, rump, uppertail coverts gray with hint of olive or yellow wash; wings and tail are olive gray. Throat white, belly and undertail coverts grayish white and flanks with hint of olive or yellow. Beak is gray and hooked at tip. Legs and feet are gray.
Adult Female (spring/summer)
Sexes are alike and plumages similar throughout the year.
Juvenile
Duller than adults overall, more brownish, with very pale cinnamon or buffy wing-bars.
General:
Plain, medium sized Vireo. Length 12-13cm. Wing: 22cm. Weight: 10-16grams.
Behaviour:
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 is found 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. The clutch is 3-5 dull white, heavily spotted eggs. Both parents share nest building and caring of the young.
Similar species:
Philadelphia Vireo, Red-eyed Vireo, Hutton’s Vireo, Cassin’s Vireo
Conservation Status:
Listed as Least Concern, although Breeding Bird Survey data shows declines in California, Michigan, Ohio, West Virginia and Wisconsin.
Capture Rates:
Capture rates 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.
Molt Summary:
PF: HY partial; PB: AHY complete; PA limited
Preformative molt includes all gr covs and often terts but no other flight feathers
The PA’s include no wing covs or flight feathers, although some inner ss (among s4 – s6) might be suspended until the PA (or next PB) in some ASYs.
From Philadelphia Vireo
Although Philadelphia Vireos have a buttery yellow wash to the breast and a more distinct facial pattern some bright Warbling Vireos can also appear very similar.
Wing morphology is however quite different. Warbling Vireo has a vestigial primary 10 (P10) shown with a red arrow in the photo below. In Philadelphia Vireo this feather is so reduced as to be almost absent.
Juveniles have upperparts brown, gr covs tipped cinnamon-buff, and underparts white. Juv M=F.
HY birds can be separated from adults by a number of criteria in addition to molt limits. The length and shape of this outermost primary (P10) tends to be longer and more rounded in HY birds (above) than adults and the upper mandible lining (roof of the mouth) pinkish to grayish white like this HY in August compared to dark grey in adults.
This HY in September is showing narrow, tapered primary coverts with narrow greenish edging contrasting slightly with the replaced and slightly fresher greater coverts, the molt limit indicated by the red arrow.
Molt limits like this can be quite subtle at this time of the year and for this reason, especially after adults of these same species begin to show signs of approaching the end of their complete prebasic molt age should always be confirmed by additional criteria such as skull ossification.
Contrast the bird above with this ASY bird in May. Notice the broad, truncate and relatively fresh primary coverts not contrasting with the greater coverts.
Notice also the shape of the vestigial outermost primary (P10) discussed above, being less rounded in adult (AHY/ASY) birds.
Another example of definitive adult plumage in spring with no discernible molt limits between the primary and greater coverts.
The tail of the ASY bird above showing relatively fresh and truncate outer rectrices with a corner to the inner web on these feathers.
Tail shape is helpful in ageing many species being tapered and more abraded on retained juvenal feathers in first year birds (HY/SY) and broad and truncate with a corner to the inner web and relatively fresh in adults (AHY/ASY). The outer retrices (R4-R6) generally show the greatest age specific differences.
However, it is important not to use tail shape alone as it is generally not very reliable because of a) individual variation and b) the possibility of accidental loss and replacement (adventitious molt). For this reason and the fact that tail feathers are frequently lost and replaced between normal molts tail feather shape must be used with great caution by banders, and only with other supporting characters (e.g., molt limits), when determining the ages of birds in hand.