The first half of the book has some terrific information but is often light on content (the equipment section, birding by geography section, finding more info section) as well as some glaring gaps (breeding habits, migration patterns, birding history in North America). It's one thing to tell a beginning birder how the gestalt of a White Crowned Sparrow is different from that of a White Throated Sparrow but does the beginning birder even know when to expect either in their area? The ending on ethics and conservation is so small it almost plays to the criticism that birders are more in it for the sport than for birds themselves.
The second half of the book is a stunning review of the external structure of birds. It is better than many ornithology texts in this regard. Everything you could ever need to know about feather structure, molt, proportional differences and color perception is presented along with an excellent introduction to taxonomy and bird song.
Sibley is obviously playing to his strength here which is fine because what he knows, he really knows if you get my point. The art work is great, of course.
I don't want to come across as knocking this book. I own it, enjoy it and have learned a great deal from it. I recommend that you buy it. I'm just not sure it will serve this generation of up and comming birders as the ideal "basics" book the way Jack Connor's "The Complete Birder" did for many in the prior generation.
What do you think of a basics book that can take the time to touch on a birds nasal bristles or gestalt but omit a basic discussion on migration or breeding? Maybe it's me but it strikes me as a bit odd. I think the second half could have been published as part of a book called "Sibley's Ornithology for Birders" or something to that effect.