The island serves as sanctuary to the threatened loggerhead sea turtle. The turtles, which can weigh up to 350 pounds, lay eggs from May to September. Other unique wildlife on the island includes wild stallions, mares, and hogs. These species are said to be feral: meaning that their ancestors were domesticated animals that have now returned to their wild state.

Much like its feral animals, Cumberland Island is also in the process of returning to its wild state. The island, established as a national seashore in 1972, is reclaiming the land. This is most evident at the Dungeness ruins. Andrew Carnegie's brother Thomas built the estate in the early 1900s. It was abandoned in the 1920s and burned down in 1959. The haunting stone ruins are now being usurped by the forest's overgrowth.