This Acadian Flycatcher was photographed in South Carolina and is used courtesy of the Hilton Pond Center for Piedmont Natural History whose website is hiltonpond 'yellow' plumage in a North American flycatchers is virtually always a sign of fresh plumage and cannot be used for the purposes of ID. (The one notable exception is Yellow-bellied FC, which is about the latest of the migrants, rarely showing up before the 3d week of May.) The Least is the earliest migrant.