A rollicking search for the origins of Inca birdman legends. Shah tracks down shamans, visits Machu Picchu, ventures out to Lake Titicaca, tackles the myths of the Nasca lines and takes hallucinogens with the Shuar in the Amazon. It's quite a tale, informative, much enlivened by eccentric characters and incident. An Afghani raised in England (where he still lives), Shah has written widely on the Middle East, Central Asia, Africa, and South America.  (PRU49, $13.95)