Do you really need another field guide to North American birds? Yes, you do. In fact, you need two of them—the sooner, the better. How many of your current field guides have entries for the Yellow-bellied Prairie Chicken, the Blunt-billed Woodpecker, or the Split Rail? None of them, I bet.
Do your current field guides explain how to correctly assemble the parts of a bird? I’m sure they don’t. Do you own a book explaining what to say to other birders while on a field trip? No? Well then…
A Field Guide to Little-Known & Seldom-Seen Birds of North America and its sequel, Another Field Guide to Little-Known & Seldom-Seen Birds of North America (both by Ben, Cathryn, and John Sill, illustrations by John C. Sill) give you this essential information.
Let me provide an example: the Texas Warbler. To quote a bit of the description,
The largest member of the genus Dendroica, this species is difficult to identify since it is the most rapid flyer. It is also the most beautiful, has the loudest song, is the most ferocious, and molts most rapidly.
My favorite bird of the bunch was the Nearsighted Bat Owl. These are quite rare because, as the book explains, “Incubation successes are generally low since every time the owl leaves the nest, the eggs fall out.”
I have found these two books to be invaluable additions to my birding bookshelf, and well worth their modest purchase prices.* The only thing lacking is a third guide. Maybe if we all ask nicely?
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* The first volume is out of print, but gently used copies are still available on line. I got mine at Amazon.com.
Mountain Plover 
Hmm….the illustration on the cover of the second one looks alot like many of my bird photos! 🙂