Ah. Colby has brought up the strange case of the missing Swainson's Thrushes: > Interestingly, ZERO Swainson's Thrushes were heard. Interestingly, in all my nights > listening (a couple dozen) in Utah, I never heard a Hermit or Swainson's Thrush in either > the spring or fall. I don't know what these birds do between the Cascades/Sierras and > the Continental Divide given my experiences thus far as I'm certainly quite baffled at this > point...
It's interesting, isn't it? In their recent monograph on the birds of western Colorado, Bob Righter et al. state the following for Swainson's Thrush: "Even during spring and fall migration, rarely found outside of breeding habitat, suggesting that most birds migrate through the mountains and mountain valleys." Coen Dexter, one of the coauthors of that monograph, put it even more dramatically to me (personal communication in front of 100+ folks when I was doing Q&A at a public talk; insert frowney-face here): There do not appear to be any credible records in western Colorado away from mountains and mountain valleys. Conversely, if you go east of the Divide, you can see 100+ per day on spring migration in Colorado. Anecdotally, that was my impression back in my Nevada days. Swainson's Thrush is common as dirt in the broadleaf forests of, say, the Ruby Mountains (northeastern Nevada). But it was notable enough in the lowlands for us to put it on the hotline. And those lowland records tended to be from the far west (Reno area) and south (Las Vegas area). I wonder if they were mainly Russet-backed (Pacific slope) birds, not Olive-backed (everywhere else) birds. Best, --Ted Floyd Lafayette, Boulder County, Colorado -- NFC-L List Info: http://www.NortheastBirding.com/NFC_WELCOME http://www.NortheastBirding.com/NFC_RULES http://www.mail-archive.com/nfc-l@cornell.edu/maillist.html --
