The Philadelphia vireo is very similar to the red-eyed and is best separated by the color of the underparts, which are always yellowish, with the strongest color on the throat. The dark lores and more greenish upperparts separate it from the warbling vireo. Philadelphia vireos are generally uncommon.
In summer they can be found in a variety of wooded habitats, usually lower than those favored by red-eyed vireos. They favor open woodlands, streamside willows and alders, and areas regenerating after fires.
The songs and calls are so similar to those of red-eyed vireos that most bird watchers cannot tell them apart with confidence. The song of the Philadelphia vireo is usually very slightly higher pitched to most ears and is slightly less rhythmic, with the phrases slightly farther apart.