Found this at amazon.com: Due out March 11, 2014.
A best seller for more than a dozen years, and now: the completely revised and updated second edition of the most comprehensive, widely acclaimed bird guide available.
Among the revisions that have been made for this second edition:
All illustrations are approximately 15%-20% larger than they appeared in the first edition.
Every image from the first edition has been re-digitized from the original art.
600 new paintings: including illustrations of 85 rare species and additional aspects of the species included in the original edition.
Two-thirds (4,356) of all original art has been revised, providing improved detail, and reflecting new physical and behavioral information.
Expanded text includes conservation status, habitat, and tips on finding species in the field.
More than 600 updated new maps.
Elegant overall new design.
FYI: the page count has increased from 544 to 624.
David Sibley has been working on a revised edition of his bird guide. It's due out in 2014. Here's are sample plates:
To see the artwork in progress, click here