Like all birds, Vireo philadelphicus perceives the environment through visual, auditory, tactile and chemical stimuli. This species communicates inter- and intraspecifically using calls, body postures and physical encounters. The typical Vireo philadelphicus call, given only by males, is mnemonically described as "cherrie-o-witt, cheree, sissy-a-witt, tee-o". This is very similar to that of red-eyed vireos but it is frequently higher-pitched with longer pauses between phrases. Both males and females use a harsh "ehh" call in response to intruders or between mates.
Typical warning body postures include erecting crest feathers, fanning tail feathers, gaping the beak or holding the head low with body horizontal. These are typically used to warn off intruders and a physical attack may follow if the intruder does not retreat. Vireo philadelphicus is typically not aggressive, but will aerially chase, peck, or grapple with threatening individuals.
Currently, known courtship rituals solely consist of body postures. Males will erect crest feathers, fan their tails, and rarely sway back and forth. Females will respond or initiate these rituals with crouched wing-quivering.
Communication Channels: visual ; tactile ; acoustic
Perception Channels: visual ; tactile ; acoustic ; chemical
Currently, Vireo philadelphicus is of least concern to the IUCN Red List due to an increasing population size and abundance over a large geographic range. They thrive in successional forests that are currently created nearly exclusively by human disturbance, specifically select harvesting or clear-cutting. Due to their preference for white ash and yellow birch, harvesting of these species may negatively affect their populations.
US Migratory Bird Act: protected
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
There are no known adverse effects of Vireo philadelphicus on humans.
Vireo philadelphicus's consumption of wood-boring beetles and caterpillars during outbreaks indirectly affects humans by protecting trees which are used for harvest, oxygen production, or prevention of soil erosion.
As primarily an insectivore, Vireo philadelphicus likely impacts the local insect communities, especially during times of caterpillar outbreaks. They also consume wood-boring beetles which reduces damage to local trees. Vireo philadelphicus nests are occasionally used by parasitic brown-headed cowbirds. Parasites that utilize Vireo philadelphicus are currently unknown.
Commensal/Parasitic Species:
Vireo philadelphicus is primarily an insectivore but will seasonally eat berries. Berries constitute 7% of the diet year-round, but up to 20% of the diet during winter. They are gleaners and prefer to capture insects from leaves while flying by or hovering. Philadelphia vireos have been shown to prefer foraging on white ash and yellow birch, specifically. The most frequent dietary item is caterpillars and Philadelphia vireo populations may increase in response to a high abundance of caterpillars. Double broods have been reported in some years of caterpillar outbreak. Other dietary items include: butterflies and moths, beetles, ladybugs, leaf-eating beetles, weevils, wood-boring beetles (Buprestidae and Cerambycidae), click beetles and flies.
Animal Foods: insects; terrestrial non-insect arthropods
Plant Foods: fruit
Primary Diet: carnivore (Insectivore )
Vireo philadelphicus, or Philadelphia vireos, inhabit the Nearctic and Neotropical regions. These birds breed across southern Canada and select northern portions of the United States. Philadelphia vireos overwinter in Central America from southern Mexico through Panama. Their migration range covers the Gulf Coast and the eastern half of the United States, excluding the southeast.
Biogeographic Regions: nearctic (Native ); neotropical (Native )
Vireo philadelphicus primarily breeds in the boreal forests of southern Canada. They may also breed in second growth or early- to mid- successional forests composed of aspen, birch, alder and ash trees. They seem to prefer dense habitats with complex vertical structure, as well as 70 to 100% canopy closure. During migration these birds may be found in similar habitats, but more often in dense, shrubby thickets. While wintering in Central America, this species is often found along scrubby edge habitats and occasionally in plantations or gardens. They have been recorded at elevations of up to 1,600 m in Central America.
Range elevation: 1,600 (high) m.
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: forest
Other Habitat Features: agricultural
The longest-lived Vireo philadelphicus was 8 years and 10 months old. Little is known regarding causes of mortality for this species. They are occasional hosts to parasitic brown-headed cowbirds, but this does not cause significant damage to population numbers. Some fatalities occur during migration from impact with television towers, though this is also not thought to be a significant cause of mortality.
Range lifespan
Status: wild: 10.6 (high) years.
Vireo philadelphicus are small, stocky vireos that appear very similar to Vireo olivaceus. Philadelphia vireos measure 13.3 cm in length, have a wingspan of 20.3 cm, and weigh in at only 12 g. Like all vireos, they feature a distinctive slender, hooked beak which in Philadelphia vireos is shorter than most other vireo species. They have olive-gray backs and wings, with a gray-blue cap. They feature thick white supercilia, dark gray eye-stripes and dark lores. Undersides are a mix of bright and dull yellow, with the brightest yellow at the throat. Their tails are olive-gray and relatively short. Legs and beaks are slate gray to black in color. This species exhibits no sexual dimorphism and juvenile plumage is not distinctive.
Philadelphia vireos are often confused with red-eyed vireos and warbling vireos. Red-eyed vireos are larger, with longer beaks and lack the bright yellow throats and undersides of Philadelphia vireos. Warbling vireos have paler facial features and paler underparts. The brightest yellow is on their flanks, and their throats are white as opposed to yellow.
Average mass: 12 g.
Average length: 13.3 cm.
Average wingspan: 20.3 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: sexes alike
No observations of predation on Vireo philadelphicus have been made. Vireo philadelphicus does exhibit mobbing behavior in response to potential predators and has been observed mobbing blue jays, squirrels, and common grackles. The olive-gray coloration of these vireos likely serves as camouflage in the dense canopies they inhabit.
Anti-predator Adaptations: cryptic
Vireo philadelphicus is a monogamous species, but mate or site fidelity has not been studied extensively. Pairs form soon after arriving at the breeding grounds or possibly during migration. Courtship often consists of males snapping their bills, tail-fanning and erecting crest feathers. Females respond to or initiate this ritual by wing-quivering. Males will follow their mates and actively defend them from other males. These vireos display little aggression between mates compared to closely related Vireo olivaceus.
Mating System: monogamous
For Vireo philadelphicus, the breeding season occurs annually between May and August. These vireos depart from the wintering grounds relatively late and typically do not arrive on the breeding grounds until late May. Males begin singing in early June and pair-formation occurs two weeks after arrival. After pair-formation, females begin searching for suitable nesting sites with their respective mates following close behind to defend them from intruding males. The female selects a forked branch high in the tree canopy, typically 9 to 24 m above the ground. Females alone construct the hanging, cup-shaped nests and use birch bark, grass, feathers, vegetation and spider webs as materials. Typical clutch size is 4 but may range from 3 to 5. Eggs measure 19 mm in length and are white and speckled with brown or black.
Both males and females perform incubation and thus males feature a small brood patch during this time. Incubation lasts 11 to 13 days, after which the altricial young are fed and brooded by both parents. At 12 to 14 days after hatching, the young fledge but remain with the parents for an additional 10 days. The age at which juvenile Philadelphia vireos reach reproductive maturity is unknown.
Breeding interval: Philadelphia vireos breed once yearly.
Breeding season: Philadelphia viroes breed from May through August.
Range eggs per season: 3 to 5.
Range time to hatching: 11 to 13 days.
Range fledging age: 12 to 14 days.
Range time to independence: 10 (low) days.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
Parental investment begins with time, energy, and risk involved with selecting and defending nesting territory or mates. After mating occurs, females select a suitable microhabitat in which to construct a protected nest. Both males and females incubate the clutch and males develop a small brood patch. After the clutch hatches, both parents gather food to provide the altricial young. Parents often forage outside their typical area which puts them at risk for interspecies aggression or predation. Philadelphia vireos often nest alongside more aggressive red-eyed vireos which will attack any intruder to their territory. Philadelphia vireos often have to defend their nests and young from aggressive encounters with these close relatives. Once the young fledge, parents continue to provide care for at least an additional 10 days. If red-eyed vireos are nesting nearby, the parents must actively defend their defenseless fledgers against aggressive red-eyed vireos that perceive the fledgers as intruders. Observations have been made of young Philadelphia vireos being ushered by parents from open areas to nearby shrubs for shelter.
Parental Investment: altricial ; male parental care ; female parental care ; pre-fertilization (Provisioning, Protecting: Male, Female); pre-hatching/birth (Provisioning: Male, Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female)
