Philadelphia Vireo

Like several other species that breed in low densities in northern New Hampshire, the Philadelphia Vireo is most frequently encountered during migration. It is seen here almost entirely in fall, since spring migration occurs primarily west of the Appalachians. It is never common here, and information on population trends is confounded by problems of identification (see below). Outside of migration, you are most likely to encounter this species in northern Coos County, although small numbers occur south into the White Mountains.

Finding Philadelphia Vireos in New Hampshire is complicated by identification challenges. They are typically the yellowest of our vireos, but observers need to be wary of bright Warbling Vireos in the fall. The definitive way to separate the two species is by the Philadelphia’s dark lores – the area between the eye and the bill. This makes it look like there’s a line going through the eye, while in Warbling Vireos the face looks far more pale.

During the breeding season the identification problem shifts to song. By all accounts, the song of the Philadelphia Vireo cannot be reliably distinguished from that of the far more common Red-eyed. For this reason, you’ll need to see the singer to get a conclusive ID. Your best bet for a Philadelphia in this season is in forest edges and second growth rather than the canopy of mature trees. Studies of the two species where they co-occur have revealed that they often exclude one another from their territories, and the similarities in their songs support this. There are even records of hybrids between the two.