The hot, humid lowland between the Eastern Sierra Madres and the Gulf of Mexico, including northern Chiapas, harbors the greatest diversity of bird species among all of Mexico's biological regions. Until now we've not seen a single species that in Mexico is restricted to the Gulf lowlands.

But in this list we have three "Gulf-Coast specialist" species -- the Rufous-tailed Hummingbird, Black Robin and Yellow-winged Tanager -- which amounts to 21% of the list. As we drop lower the percentage should increase. Often species restricted to Mexico's Gulf coast extend on southward through the Caribbean lowlands of Central America into northern South America. Now we're getting into country that's famous not only for its quantity of birds but also its exotic variety, and the more we descend the better it'll get.