On the breeding grounds, Philadelphia Vireos use thickets of regenerating woodlands, including aspen, birch, alder, cherry, ash, willow and alder along streams, and sometimes black spruce and balsam fir. In the easternmost part of the breeding range, they are birds of the poplar and birch canopy, especially in woodlands with alder in the understory. Farther west, look for them in aspens with understory of paintbrush, fireweed, highbush-cranberry, alder, willow, and clover. On migration, they tend to select similar second-growth habitats, regenerating burned areas, riparian thickets, and other habitats offering young trees with some undergrowth, especially near water. Likewise, on the wintering grounds, Philadelphia Vireos use many kinds of second-growth and edge habitats, from lowland gardens and mangrove forests to shaded coffee and cacao plantations at higher elevations (up to about 5,250 feet elevation). Back to top
Philadelphia Vireos eat mostly insects and some fruit. Main prey include caterpillars in the warmer months (breeding season and early fall migration), as well as spiders, weevils, wood-boring beetles, leaf-eating beetles, click beetles, wasps, bees, ants, bugs, moths, and flies. They generally forage in upper parts of trees, picking prey from foliage and leaves or occasionally on short flights (they normally forage higher than Red-eyed Vireos). They also take insects from branches and trunks but rarely from the lowest parts of the tree or the ground. Migrants and wintering birds eat berries and seeds of many sorts. Back to top
Females select the nest site, usually near the top of a small tree, 8–65 feet high, with the average being 50 feet. They may nest in aspen, birch, maple, or alder. The nest is suspended from a forked branch, usually fairly close to the trunk.
The female builds the nest accompanied by the male, who occasionally assists. The nest is constructed from bark strips, grasses, seed tufts, feathers, and beard-moss lichen, and is lined with pine needles and grass blades. Nests measure on average 2.8 inches across, with the interior cup about 2 inches wide and deep.
|Clutch Size:||3-4 eggs|
|Number of Broods:||1 brood|
|Egg Length:||0.7-0.8 in (1.78-2.17 cm)|
|Egg Width:||0.5-0.6 in (1.3-1.53 cm)|
|Incubation Period:||11-13 days|
|Nestling Period:||14-15 days|
|Egg Description:||White and spotted with rusty, dark brown, or black.|
|Condition at Hatching:||Helpless and blind, with orange-yellow skin and sparse, pale-gray down.|
Philadelphia Vireos typically arrive in late spring on the breeding grounds; both sexes arrive at the same time and begin to establish territories. In some cases, actual nesting may not begin for several weeks, perhaps delayed until weather and prey conditions are suitable. Courting males quiver the wings, fan the tail, erect the crown feathers, sway, preen, and snap the bill; an interested female responds by dropping and vibrating the wings. The species is socially monogamous. Although apparently less aggressive than Red-eyed Vireos, Philadelphia Vireos vigorously defend territories (up to about 10 acres) sometimes even against the larger Red-eyed. Males guard females through courtship, nest-building, and egg-laying phases, driving away other males by threat postures, chases, and attacks. Both sexes feed and tend the young. During migration and on wintering grounds, Philadelphia Vireos join mixed flocks of woodland birds when foraging.Back to top
Philadelphia Vireo populations increased by about 2.3% per year from 1966–2015, according to the North American Breeding Survey. Partners in Flight estimates a global breeding population of 4 million and rates the species a 9 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. The population increase could be attributable to forest management practices that have increased nesting habitat. Philadelphia Vireos, like most songbirds that migrate nocturnally, often strike buildings, cell towers, and other lit structures, making Lights Out initiatives in cities an important conservation approach. On Central American wintering grounds, widespread conversion of forest to pasture has reduced habitat available to them there.Back to top
Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.
Moskoff, William and Scott K. Robinson. (2011). Philadelphia Vireo (Vireo philadelphicus), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.
Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.
Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2017). The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 2.07.2017. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.
Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.