Excellent background info before visiting El Cielo
I bought two copies of this in preparation for a group birding trip to El Cielo, southern Tamaulipas state, in Nov 2018. This is a memoir by the Websters which includes an interesting historical overview of this area in the Sierra Madre Oriental. Sadly, there is no index and the book could use some decent maps.
There is now a modern environmental center on the outskirts of Gómez Farias (our base for four nights), with a lovely tiled cistern between informational exhibits, a large parrot enclosure and museum buildings. Also visited Alta Cima.
If you are heading to this area, read this book.