Science! Science reporting at its finest. Very well-sourced, with outstanding, quotes, commentary, and links. The full study referenced is available for perusal. I highly recommend doing so as it further and more deeply elucidates the subject matter. The Author's style here is breezy yet authoritative without being overbearing or pedantic. No blatherskite she. A fascinating subject made even more so by the Writer's apparent enjoyment at having taken up the topic. Well done! And, a must-read for amateur birders, like myself. Five stars!