Cross posting from science forum in case you missed it:
http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=228x27566Highlighted quotes:
"Genetic tests of North American birds show what may be 15 new species including ravens and owls -- look alikes that do not interbreed and have wrongly had the same name for centuries, scientists said on Sunday."
"Look alike species were of the Northern Fulmar, Solitary Sandpiper, Western Screech Owl, Warbling Vireo, Mexican Jay, Western Scrub-Jay, Common Raven, Mountain Chickadee, Bushtit, Winter Wren, Marsh Wren, Bewick's Wren, Hermit Thrush, Curve Billed Thrasher and Eastern Meadowlark."
"They said DNA diverged by at least 2.5 percent -- enough, they said, to define a species despite almost identical shape, plumage and song. A one percent difference typically indicated a million years without interbreeding, they said."
"The study also found 14 pairs of birds with separate identities that were almost genetic "twins", two trios of birds were DNA triplets and eight gull species were almost identical.
"Some of these on close inspection may really be better considered as a single species," said Stoeckle. "Others are probably very young species at the borderline."
The Snow Goose and Ross's Goose, for instance, shared 99.8 percent of DNA and the black-billed magpie and the yellow-billed magpie 99.6 percent. Gulls such as the Glaucous and Iceland Gulls were 99.8 percent the same."
So here's the problem for US:
If you have two separate species of a bird that look and sound and act exactly alike, how do you ID it in the field?