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.
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. (Bennett, et al., 2000; Moskoff and Robinson, 1996)
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. (Ehrlich, et al., 1988; Moskoff and Robinson, 1996; Sibley, 2000)
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. (Ehrlich, et al., 1988; Moskoff and Robinson, 1996)
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. (Ehrlich, et al., 1988; Moskoff and Robinson, 1996)
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. (Moskoff and Robinson, 1996)
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. (Moskoff and Robinson, 1996)
Vireo philadelphicus is a neo-tropical migratory species that performs two migrations annually: one in spring and another in fall. During the breeding and non-breeding seasons this species is diurnal but like most songbird migrants, they migrate at night. During migration and non-breeding seasons, these vireos will form groups with other migratory species including warblers and other vireos. They are an arboreal species that forages and nests within tall canopy trees.
Vireo philadelphicus forms pairs during the breeding season and defends feeding and nesting territory by singing advertisements and occasionally physical aggression. Males sing on their territories and warn intruding birds using body postures. These warning postures include raising the crest feathers, perching with head thrust forward and beak agape, and fanning the tail feathers. Both sexes produce a harsh 'ehh' sound when intruders are near or as a contact call between mates. Males will chase intruders away or even attack and grapple if the intruder is persistent.
Interspecific competition with red-eyed vireos often occurs as they prefer to breed in similar habitats. When both species are present, aggressive encounters are frequent and there is significant resource competition. Slight resource allocation occurs in that Philadelphia vireos forage and nest in the highest canopy layer, while red-eyed vireos tend to remain in the middle canopy. Philadelphia vireos also prefer white ash and yellow birch as canopy species, whereas red-eyed vireos are very broad in their habitat use and will utilize any available species. (Moskoff and Robinson, 1996; Robinson, 1981)
Territory size for Philadelphia vireos varies in response to population density and resource availability. Size has been recorded ranging from 0.3 to 0.8 hectares. (Moskoff and Robinson, 1996)
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. ("Whatbird.com: Field Guide to Birds of North America", 2007; Moskoff and Robinson, 1996)
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. (Ehrlich, et al., 1988; Moskoff and Robinson, 1996; Robinson, 1981)
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. (Moskoff and Robinson, 1996)
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. (Moskoff and Robinson, 1996)
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. (Moskoff and Robinson, 1996)
There are no known adverse effects of Vireo philadelphicus on humans.
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. ("Birdlife International", 2009; Moskoff and Robinson, 1996)
Rachelle Sterling (author), Special Projects, Tanya Dewey (editor), University of Michigan-Ann Arbor.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the southern part of the New World. In other words, Central and South America.
uses sound to communicate
living in landscapes dominated by human agriculture.
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
Referring to an animal that lives in trees; tree-climbing.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
active at dawn and dusk
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
parental care is carried out by females
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
An animal that eats mainly insects or spiders.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
parental care is carried out by males
makes seasonal movements between breeding and wintering grounds
Having one mate at a time.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
2009. "Birdlife International" (On-line). Vireo philadelphicus. IUCN Red List of Threatened Species. Accessed March 28, 2011 at http://www.iucnredlist.org/apps/redlist/details/146470/0.
2007. "Whatbird.com: Field Guide to Birds of North America" (On-line). Philadelphia vireo. Accessed March 28, 2011 at http://identify.whatbird.com/obj/693/_/Philadelphia_Vireo.aspx.
Bennett, S., P. Sherrington, P. Johnstone, B. Harrison. 2000. Habitat Use and Distribution of Listed Neotropical Migrant Songbirds in Northeastern British Columbia. Proceedings of a Conference on the Biology and Management of Species and Habitats at Risk, 1: 79-88.
Ehrlich, P., D. Dobkin, D. Wheye. 1988. The Birder's Handbook: A Field Guide to the Natural History of North American Birds. New York, New York: Simon & Schuster Inc..
Moskoff, W., S. Robinson. 1996. "Philadelphia Vireo (Vireo philadelphicus)" (On-line). The Birds of North America Online. Accessed March 27, 2011 at http://bna.birds.cornell.edu/bna/species/214 doi:10.2173/bna.214.
Robinson, S. 1981. Ecological relations and social interactions of Philadelphia and red-eyed vireos. Condor, 63: 16-26.
Sibley, D. 2000. The Sibley Guide to Birds. New York: Alfred A. Knopf, Inc..