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"New advances are presented in the field identification of Long-billed and Short-billed Dowitchers in worn alternate and basic plumages. Emphasis is placed on scapular and covert feather patterns and structural features in conjunction with a combination of other "soft" field marks. One newly discovered structural feature is a difference in "loral angle", which is a measure of how high the eye is positioned above the extension of the gape. Long-billeds have a more acute loral angle than Short-billed, giving the former a straighter-looking supercilium and the latter a more arched supercilium. These structural differences are speculated here to be an evolutionary manifestation of their fundamentally different habitat preferences on breeding grounds."
Link: Full Article from Surfbirds.com
After you've read the article, take a guess on the ID of the pictured dowitchers!
Dowitcher image © 2005 Michael McDowell