Date: 9/19/26 11:37 am From: Jacob C. Cooper via groups.io <cooperj2...> Subject: Re: [NEBirds] Philadelphia Vireo
Hi Robin,
The Philadelphia Vireo is part of the gilvus clade of “Warbling Vireos”, which now includes the two Warbling-Vireos as well as the Neotropical Brown-capped Vireo. Philadelphia appears to be most closely related to Brown-capped, but it I know that there is more work that should be done on Brown-capped, especially given its broad range in the Neotropics. (https://doi.org/10.1016/j.ympev.2014.07.021)
Philadelphia Vireos mimic Red-eyed Vireos on the breeding range, as a form of social mimicry (similar to Downy + Hairy Woodpecker). From Birds of the World, my emphasis added:
"Philadelphia Vireo imitates the song of Red-eyed Vireo, although the former's song is structurally less complex (Rice 1978b, Rice 1978c). Unlike Red-eyed Vireo, Philadelphia Vireo discriminates between its song, that of Red-eyed Vireo, and songs with modified syntax (Rice 1978b). Playback experiments confirm that because Philadelphia Vireo is considerably smaller than Red-eyed Vireo, it has an incentive to avoid interspecific hostilities (Rice 1978b). The similarity in songs of the 2 species constitutes a form of social convergence in which Philadelphia Vireo can advertise/defend territories without having to confront Red-eyed Vireos physically. Social mimicry thereby maintains interspecific territorial integrity (Rice 1978b)." (https://doi.org/10.2173/bow.phivir.01)
Assistant Professor, University of Nebraska at Kearney
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2401 11th Avenue
Kearney, NE 68849-1130
Research Associate, Field Museum, Chicago
Citizen of the Cherokee Nation
From: <NEBirds...> <NEBirds...> on behalf of Robin Harding via groups.io <pine2siskin4...>
Date: Saturday, September 19, 2026 at 08:19
To: <NEBirds...> <NEBirds...>
Subject: [NEBirds] Philadelphia Vireo
Caution: Non-NU Email
Nebraska birders,
When I reviewed my comments on the Philadelphia Vireo seen at Hall County Park, I realized that I had made a mistake. In my comments, I wrote "the eye line was darker than red-eyed vireo." What I had intended to write is "the eye line was darker than Warbling Vireo." I edited my comments on my ebird list.
In the past, I may have seen a Philadelphia Vireo but thought it was a Warbling Vireo. I'm glad that I was with other birders who had some experience with Philadelphia Vireo.
Do you know where I can read more about vireo evolution? Is Philadelphia Vireo a hybrid that has become a species? It looks like a cross between Warbling and Red-eyed. I'm not familiar with Philadelphia's song, but I've read that it is very similar to Red-eyed. So it looks like a Warbling Vireo and sings like a Red-eyed Vireo. What's going on here?
