Mandeville is known for its gardens and I don't know of any specific place for bird watching there but anywhere you find flowers or water or gardens, you will find birds.

As for your "Ivory Bills", most woodpeckers tend to be less visible in the summer as they are busy feeding their young and don't wish to be seen doing so. Predators etc could follow them to their nests. A good book to read about the Ivory Bill is "The Grail Bird". The book is all about the trek into the Arkansas swamp in search for the Ivory Billed Woodpecker. The bird was once know as the "Lord God" bird because it is so big and when seen flying people would say . . . "lord god, that's a big bird".