For all but a handful of her 84 years, Jeannie David has lived beside the bayou, the one locals say Louisiana’s founder, Pierre Le Moyne d'Iberville, named for a friendly man they say had an unusually large head — or, as the French put it, a “Grosse Tete.” David’s screened porch overlooks Bayou Grosse Tete, where she and her husband watch the constant hum of life. They count turtles sunning on logs, sometimes dozens at once. Fish jump, water snakes glide over the surface and herons wade.