Mysticete
Well-known member
The Warbling Vireo possesses differences in song and genetics (IIRC, barcode data suggested more than one taxa). I think there are some slight differences in morphology, although they are very slight indeed and probably not terribly useful in the field.
Just for fairness, I think there are a few potential lumps in the future as well. The validity of Northwestern Crow and the NA Rosy-finch splits is somewhat questionable.
And to add in a few more, I would add Mountain Chickadee, Brown Creeper, and Bewick's Wren to that list. And the Yellow Warbler complex, which has already been partially split by IOC
Just for fairness, I think there are a few potential lumps in the future as well. The validity of Northwestern Crow and the NA Rosy-finch splits is somewhat questionable.
And to add in a few more, I would add Mountain Chickadee, Brown Creeper, and Bewick's Wren to that list. And the Yellow Warbler complex, which has already been partially split by IOC