According to the publisher, The American Bird Conservancy Guide to Bird Conservation is "the most authoritative book on bird conservation in the Americas ever published".
It's true: this book is comprehensive. Within its pages are species accounts of all conservation "WatchList" species from the United States. Its American bias is perhaps unfortunate, but nevertheless the book remains substantially applicable to Canada as well. Also, the treatment of Hawaiian birds was very eye-opening (Hawaii has the most endemic bird species and has experienced the most bird extinctions by far of any US State or Canadian Province/Territory).
Although I read it cover-to-cover, this is really more of a reference book. Many of the threats and issues of concern to bird conservationists are common to many species, so you will find that if you read it in a linear fashion the book does become repetitive. On the other hand, the information provided is thorough and some of the repetition allows you to draw connections and see commonalities where they exist between different bird species. This book also includes a discussion of the Neotropics, which is not only a location of conservation concern for our migratory species, but also for its own resident bird species and populations.
On the binocular scale, from Tasco on the low end to Swarovski at the high end, I rate The ABC Guide to Bird Conservation as a Nikon. Not really necessary reading, but innovative and well done.