The J. N. "Ding" Darling National Wildlife Refuge is located on the subtropical barrier island of Sanibel in the Gulf of Mexico. The refuge is part of the largest undeveloped mangrove ecosystem in the United States and is world famous for its spectacular migratory bird populations. J. N. "Ding" Darling is one of over 540 refuges in the National Wildlife Refuge System administered by the U. S. Fish & Wildlife Service.