My book arrived today, and I think this must be the printed field guide of any sort with the highest ratio of info per weight or volume. It even came in a letter-size padded envelope. I did not believe my eyes when I opened it and saw the book. There is a surprising amount of info regarding field identification. The illustrations are somewhat basic, but they are very much better than I expected. Though I would not want to identify a tinamou solely with this book. And the Dunlin looks somewhat confusingly similar to the Pectoral Sandpiper next to it. In part because the illustrations on the same page are not to scale. So there are definite limitations, also due to the fact that there is very limited info on voices.
The book relies heavily on the annotated pointer system as used by Svensson et al in the so called "Collins" for European birds.
Despite its compact size, the book has range maps. And they are quite legible with the exception of species that have a very restricted range or when the range is a very narrow band in the Andean foothills (e.g. Black-mandibled Toucan).
The dimensions given in the product details are correct except for the thickness of the book. It should read 1,4 cm. Still extremely slim, however.
Overall, I think this is a superb buy, and the authors and illustrators are to be congratulated. One does really get a fine overview of the avifauna of Colombia. Something that I have not as easily managed from the "Birds of Northern South America". Also, those two books would be way too bulky for taking them into the field.
I give the book five stars not because I think it is the best possible field guide, but because of its fine combination of info and size.