Hi Folks! Sam is referring to a numeric list Marshall andf I use in our database. 710 = Solitary Vireo [all forms] 711 = Blue-headed Vireo [undifferentiated] 711.1 = Blue-headed [Vireo solitarius solitarius] 711.2 = Mountain Vireo [Vireo solitarius alticola] 712 = Plumbeous Vireo 713 = Casson's Vireo We know very little about the regional differences between Blue-headed Vireo and Mountain Vireo. Do Not Assume that a "Blue-headed Vireo" in Garrett County is a Mountain Vireo; Do Not Assume a "Blue-headed Vireo" away from Garrett is a Blue-headed Vireo. None of the field guides will help you. You must learn to distinguish these by yourself. Look at and listen to each migrant "Blue-headed Vireo" carefully this Spring. Look and listen to the ones that breed in Garrett. Decide for yourself if you can distinguish them. Good Birding! Jim Jim Stasz North Beach MD jlstasz@aol.com