WATERBIRDSThe book John James Audubon would have made if he had used a camera. Brushing aside rattlesnakes on Green Island, Texas, or enduring the bitter cold of an Alaskan winter, Theodore Cross has pursued waterbirds with passion. On four continents, from the tundra of eastern Siberia to the tropical islands of the South Pacific, he has captured elegant and unusual birdsfrom auklets and egrets to gannets and sanderlingsin peak action, be they courting,