GCBO Bird of the Month

Philadelphia Vireo

by Mike Williams


The Philadelphia Vireo, (Vireo philadelphicus), was first described by John Cassin in 1851 from a collected sample that originated in Philadelphia. Its is member of the family Vireonidae and the genus Vireo and are related to crows and babblers, (babblers are likely the old world equivalent to the new world Vireos). Recent study shows a strong relationship to Shrikes. The genus Vireo has 34 members currently, the Philadelphia being one of 4 in the gilvus group. This group contains the closely related Warbling Vireo as well as the Tepui and Brown Capped Vireo.

The Philadelphia Vireo breeds in Central and Southern Canada and Winters in the Yucatan and Central America. It is almost entirely migratory but found extensively throughout the Eastern and Central US during this time.

Preferred habitats include open woodlands, clearings, and thicket but during migration can be found in varied habitat.

Philadelphia Vireos typically nest in trees of mid height and construct a nest of moss, lichen and plant material hung with spider silk 10-90 feet up. 3 -4 white speckled eggs are laid and are incubated for 11-13 days by both parents with the young fledging after a further 2 weeks.

The Vireo’s diet is typically insect based but they do eat berries particularly in the fall. They do forage and will even take prey while hovering. 


A small, short beaked vireo with olive green to grey upperparts, and white to yellowish underparts with a yellow throat. They have a light face contrasting with a slightly dark cap. There is a discernable eye stripe. Note the similarity to Warbling Vireo and the two are often confused but Philadelphia’s are always more yellow.

Its song is a whistled 3-5 notes repeated over and over with a gap of 2-3 seconds between each phrase.

Its call is a repeated “weezh weezh weezh”.

Interesting Facts:


·      Philadelphia Vireos are seldom found in the city of Brotherly Love

·      Philadelphia Vireos are found further North than any other vireo

·      They can co-exist with Red Eyed Vireos and will modify their aggressive behavior to do so.

·      A group of Vireos is known as a Call

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