The Warbling Vireo is one of three migratory vireos that are regular summer residents of Washington. Although it is a common breeding bird of much of Washington, it is not known if it breeds in Edmonds. It definitely spends time in Edmonds as it migrates through the area in May and as it returns south from late July through mid-September. Look for this bird where there are streams, ponds, or marshes with corridors of tall deciduous trees such as at Yost and Pine Ridge Parks, Southwest County Park, and Willow Creek Hatchery.
The canopy of large deciduous trees is the preferred habitat of the Warbling Vireo. It eats mainly caterpillars, pupae and adult moths and butterflies. It also eats other insects. In fall and winter it adds bunchberries, elderberries, poison oak berries, sumac, and other fruits to its diet. It tends to be slow moving when it forages for caterpillars and other insects. It gleans them from leaves and twigs in tree tops, but it will also hover, hawk, and flycatch, depending on available prey. Pairs forage alone during breeding season. At other times individual birds can be found in mixed-species feeding flocks.
The male defends its territory with song. His courtship displays involve strutting and hopping around the female with his wings spread and his tail fanned. Although the female does most of the work, both sexes build the nest of plant fibers, grasses, and bark strips. The nest is a deep cup, suspended by its rim from a forked twig. The western population of this species often places its nest in a shrub or tree within 30 feet of the ground. Both sexes incubate the three to five eggs for about two weeks. The female incubates overnight while the male sleeps in a nearby tree. The male often sings from the nest. Both parents feed the nestlings. The young birds fledge at about two weeks of age. Brown-headed Cowbirds, which do not build their own nests, often lay an egg in a Warbling Vireo nest.
The longest-living Warbling Vireo known to researchers was a male, originally banded in 1966. It was at least 13 years and one month of age when it was recaptured and re-released during a California banding operation.
Conservation status of the Warbling Vireo is that of least concern. Between 1966 and 2014 the population increased slightly. The global population is estimated at 51 million, with 44 percent breeding in Canada, 53 percent spending part of the year in the U.S., and 87 percent spending part of the year in Mexico. It has adapted somewhat to suburban environments. Because of its preference for tall deciduous trees, the population may benefit from conifer clearcuts that leave large deciduous trees near open spaces. Thinning deciduous forests with herbicides causes steep declines in population. This species migrates during the night so population loss occurs from collisions with towers and other tall structures. Conservation of its wintering areas is critical because this species crowds into a winter range (western Mexico and northern Central America) that is disproportionately small when compared to its widely dispersed breeding range.
You can hear the song of the Warbling Vireo here: http://www.xeno-canto.org/195842.
Carol Riddell manages the bird education displays, on behalf of Pilchuck Audubon Society and Edmonds Parks & Recreation, at the Olympic Beach Visitor Station.