Like many rivers of the arid Southwest, the Gila is for much of its length a dry bed except after seasonal rains. Yet a mere century ago it hosted a thriving biological community, and two centuries ago American Indians fished from its banks. It is no mystery how the desert swallowed up the Gila. Beaver trapping, overgrazing, and woodcutting first ruined natural watersheds, then damming confined the last drops of its surface flow. Historical sources and archaeological data inform us of the Gila's past, but its bird life further testifies to the changes. Amadeo Rea traces the decline of bird life on the Middle Gila in a book that addresses the broader issue of habitat deterioration. Bird lovers will find it a storehouse of data on avian migration patterns and on ornithological classification based on skeletal structure. Anthropologists can draw on its Piman ethnoclassification of birds, which links the Gila River tribe with various other Uto-Aztecan peoples of Mexico's west coast. But for all concerned with protecting our environment, Once a River offers evidence of change that might be apprehended elsewhere. It is a case history of a loss that perhaps need never have occurred.