I generally like van Perlo's Birds of Mexico and Central America as a true field guide - that is, something to carry in the field all day every day. It's labelled an Illustrated Checklist, and has thumbnail illustrations of all the birds - including the migrants - of Mexico and Central America. It's important to have all the migrants if the guide is going to be at all useful to those who are not already familiar with the birds of the USA and Canada which migrate or winter in the region but are often omitted in other field guides for Mexico. This would be a useful tool for conservation in the region except the text is in English. A Spanish edition would be a great improvement.
The problem is that there are few illustrations of immatures and there are many errors in the book. I need to start collecting the errors in one place and decided to do it here. When you find others, please let me know.
Unofficial errata - B. van Perlo, Birds of Mexico and Central America
97.15 and 97.16 - Baltimore and Orchard Orioles - reversed
92.18 Lined Seedeater range SMeCAm actually vagrant to Panama
90.17 Blue Grosbeak, not Grosbeak.
Chimney Swift 44.8 map p. 260 - completely wrong
Golden-fronted Woodpecker 54.12 map p. 269 does not include Northeast Mexico
Tawny-crested Tanager 88.7 p. 298 - completely wrong