Finally, guidebooks that take eco-tourism seriously. John Muir Publications debuts its new Adventures in Nature series this month with guides on Belize and Guatemala ($18.95 each). The books are as indispensable for first-time visitors as they are for wildlife lovers. Birders, snorkelers, fishermen, archaeologists, and botanists will find extensive lists of the best outfitters and preserves. Itineraries cover everything from volcano hikes to walks through sacred Mayan caves and butterfly breeding grounds. Written by environmentalists Richard Mahler and Steele Wotkyns, this series is outstanding in its depth of information about conservation issues.