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Title: Sibley Guide to the Birds solves common indentification problem
Review: Most field guides due to size constraints limit the number of plumage phases. The Sibley guide gives many more illustrations. I was startled to see how many different phases there are to many birds particullary the Bald Eagle. I would reccomend this book to any serious bird watcher. No, I don't expect anyone to carry it into the field but studying it before and after a field trip could help in identifying a difficult sighting.
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