In the tropical wetlands and escarpments of Kakadu National Park, the seasons move from dry to wet to dry again. Those seasons have shaped the astonishing variety of plants, animals, birds, insects, migratory birds by the thousands, grasshoppers and owls, lizards and turtles, fruit bats and spear grass. And, gliding past them all in the rivers and waterholes, the long, sinuous shapes of crocodiles.