Basics: 2004, softcover, 192 pages, 70 color plates of 600 species, no range maps
Like several other books by these authors, this book is a select, reduced version of their original work "A Guide to the Birds of India, Pakistan, Nepal, Bangladesh, Bhutan, Sri Lanka, and the Maldives" of 1999. This Bhutan book is a true field guide sized option that illustrates all 600 species found in the country.
The plates illustrate the birds quite well and are usually shown with multiple plumages when significant differences exist between genders, age, or subspecies. These illustrations are good enough to identify most species. Each plate contains 3-14 species, made up of 8-25 illustrations. The plates for the raptors are somewhat crammed with many smaller illustrations, but they are still decent enough to work for identification.
Like the Southern, Northern, and Nepal counterparts to this book, the text is the weaker element. Each bird receives 3-15 lines describing it. This text may not always be sufficient to differentiate between many of the more similar birds. Sometimes a line or two is offered about the habitat or distribution. The raptors receive the most coverage while the passerines receive the least (i.e., 3-5 lines). There is only the sparsest of information given for vocalizations. Many of the birds have none. There are also no range maps.
Unfortunately, missing from this book are the several appendix-tables found in the three other sister books. Those tables helped to supplement the relatively thin text on identification. They provided a comparison list of the more difficult bird groups such as nightjars, warblers, rosefinches, and the Yellow and the White Wagtail.
For Bhutan, this book is probably your second best option, aside from the author's combined Birds of India that use the same plates. A superior, but more expensive book is the "Birds of South Asia" by Rasmussen.
If you're looking at other titles by these authors, Inskipp/Grimmett, keep in mind this Bhutan guide comes from the combined (but still condensed) Birds of India, which includes range maps. Basically, if you own Birds of India, you already own everything in this book. And, these two books all come from the aforementioned larger work that has everything along with extensive, in-depth text.
I've listed several related books below...
1) Birds in Bhutan: Status and Distribution by Spierenburg
2) The birds of Bhutan by Ali/Biswas/Ripley
3) Birds of Nepal, with Reference to Kashmir and Sikkim by Fleming
4) Photographic Guide to Birds of the Himalayas by Grewal/Pfister
5) Birds of India, Pakistan, Nepal, Bangladesh, Bhutan, Sri Lanka and the Maldives by Grimmett/Inskipp
6) Birds of Nepal by Grimmett/Inskipp
7) A Guide to the Birds of India, Pakistan, Nepal, Bangladesh, Bhutan, Sri Lanka, and the Maldives by Grimmett/Inskipp
8) A Photographic Guide to the Birds of India (Helm Field Guides) by Grewal/Harvey/Pfister
9) Tibet and its birds by Vaurie