Sonogram of Swainson's Thrush, followed by a Gray-cheeked Thrush and a few seconds later, a good candidate NFC for a Bicknell's Thrush over my house on 5-21-10. Initially, I thought both calls may be from a Bicknell's Thrush but recent discussion on the NFC-L list clarifies that Gray-cheeked calls can top out in mid 4 KHz's and are not necessarily indicative of a Bicknell's. Refer to the 9-19 and 9-20-11 discussion at www.mail-archive.com/nfc-l@cornell.edu/maillist.html. For even more in-depth info see Evans, W. R. 1994. Nocturnal flight call of Bicknell’s Thrush. Wilson Bull. 106:55-61 at Bill Evans Old Bird website: http://www.oldbird.org/pubs.htm