This is a very good field guide with maps showing a lot of the new distributions. The descriptions basically describe the birds and help you with the identification. The size of the book is the most ideal for the field, the drawings are good quality. Richard's book is the field guide you want to carry around in the field.

A Guide to the Birds of Costa Rica
by Dr. Alexander F. Skutch
An excellent guide, in spite of being an old publication I find this guide to be a good source of information, Dr. Skutch always surprises me with all the details he knew about birds, his knowledge of bird natural history was exceptional, the book tells you a lot! A good source to study before your trip and even good to have with during the trip although perhaps not in the field, you can leave at the hotel room for reference.