Under the theory postulated by a couple of commentors at Tweeters, we
should then assume the THREE Curve-billed Thrashers that were found 3
winters ago (2 in Montana, 1 on CBC in Saskatchewan) were captured or rode
there by human means. I highly doubt it, and repeat reference regarding
the Variegated Flycatcher two falls ago near Pasco WA AND remind everyone
that many/most of the birds in North America are from South American
lineage, at least that was my understanding of the "ornithological"
history of N. Am. Birds when I took the course under Dr. Balda in
Flagstaff AZ nearly 4 decades ago. Birds from south colonize towards
north... - Jim Greaves