Animal Diversity Web

Ge­o­graphic Range

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

Habi­tat

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)

• Habitat Regions
• temperate
• tropical
• terrestrial

• Terrestrial Biomes
• forest

• Other Habitat Features
• agricultural

• Range elevation

  1,600 (high) m

  ft

Phys­i­cal De­scrip­tion

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)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• Sexual Dimorphism
• sexes alike

• Average mass

  12 g

  0.42 oz

• Average length

  13.3 cm

  5.24 in

• Average wingspan

  20.3 cm

  7.99 in

Re­pro­duc­tion

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)

• 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. (Ehrlich, et al., 1988; Moskoff and Robin­son, 1996)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• oviparous

• 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

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)

• 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

Lifes­pan/Longevity

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)

• Range lifespan
  Status: wild

  10.6 (high) years

Be­hav­ior

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)

• Key Behaviors
• arboreal
• flies
• diurnal
• crepuscular
• motile
• migratory
• solitary
• territorial
• social

Home Range

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)

Com­mu­ni­ca­tion and Per­cep­tion

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)

• Communication Channels
• visual
• tactile
• acoustic

• Perception Channels
• visual
• tactile
• acoustic
• chemical

Food Habits

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)

• Primary Diet
• carnivore
  • insectivore

• Animal Foods
• insects
• terrestrial non-insect arthropods

• Plant Foods
• fruit

Pre­da­tion

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)

• Anti-predator Adaptations
• cryptic

Ecosys­tem Roles

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)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

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)

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

There are no known ad­verse ef­fects of Vireo philadel­ph­i­cus on hu­mans.

Con­ser­va­tion Sta­tus

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)

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• US Migratory Bird Act

  Protected

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Con­trib­u­tors

Rachelle Ster­ling (au­thor), Spe­cial Pro­jects, Tanya Dewey (ed­i­tor), Uni­ver­sity of Michi­gan-Ann Arbor.

Ref­er­ences

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..