Several years ago I had an epiphany as a bird lover, and stopped keeping my Life List. For several years before that I was an avid bird lister. Clements was always at hand, at home or on the trail or on trips. I still read that well used copy from time to time, filled with my notes and filled with memories.
Jim Clement's checklist was first published in 1972. The 6th edition was published in 2007, and includes new updates through the end of 2005, listing over 9800 species in all. The checklist is clearly organized and easy to use. Chapters are by species, with the entries arranged alphabetically by common name. Each bird's entry includes its common name, Latin name or names, habitat range, a box to check, and a line to make notes of where and when the bird was spotted.
Two indexes are provided, one of scientific names and one of common English names. There are also a list of extinct species, appendices and maps listing the distribution of bird species and endemics, major family references, and a very comprehensive bibliography.
The checklist is continually updated by the Cornell Laboratory of Ornithology. The updates are posted to the Lab's website on a somewhat erratic basis and will eventually be incorporated into the next edition of The Clements Checklist. Amazon doesn't permit a direct link to the update website; to surf there, Google on "cornell lab ornithology clements" to get to the update page. You will also find links to software to help you move your list from the 5th edition.
Unless you are a serious birder, it is hard to understand how important this book is and how hard it is to maintain and update. Check out the Preface here on Amazon to get an idea of the difficulties.
And, if you have any interest in birds, consider becoming a member of the Lab. My sales pitch appears in the first Comment.
Robert C. Ross 2008