The Sibley Guide to Birds

• As in Peterson, Sibley employs a pointer system for key field markings--but additional text blurbs are included alongside the illustrations to facilitate identification.
• Descriptive passages on identification are more detailed than those in most other field guides. For example, Sibley includes extensive information on the famously hard-to-distinguish hawks in the genus Accipiter (sharp-shinned, Cooper's, and northern goshawk), noting differences in leg thickness and wing beat that will be of use to more advanced birders. A section on the identification of "peeps" (small sandpipers) includes tips about seasonal molting and bill length. Confusing fall warblers, Empidonax flycatchers, and Alcids receive similar treatment.
• As previously mentioned, ample space is given to illustrations that show plumage variations by age, sex, and geography within a single species. Thus, an entire page is devoted to the red-shouldered hawk and its differing appearances in the eastern U.S., Florida, and California; similarly, gulls are distinguished by age and warblers by sex.
• Range maps are detailed and accurate, with breeding, wintering, and migration routes clearly depicted; rare but regular geographic occurrences are denoted by green dots.
• The binding and paper stock are of exceptional quality. Despite its 544 pages, a reinforced paperback cover and sewn-in binding allow the book to be spread out flat without fear of breaking the binding.

Some birders will be put off by the book's size. Slightly larger than the National Geographic guide, it's less portable than most field guides and will likely spend more time in cars and desks than on a birder's person while in the field. For some it will be a strictly stay-at-home companion guide to consult after a field trip; others may want to have it handy in a fannypack or backpack. But regardless of how it is used, Sibley's Guide to Birds is a significant addition to any birding library. "Birds are beautiful," the author writes in the preface, "their colors, shapes, actions, and sounds are among the most aesthetically pleasing in nature." Pleasing, too, is this comprehensive guide to their identification. --Langdon Cook