Amazingly, this remarkable birding hotspot did not even exist 25 years ago! Once the southern portion of North (or Nauset) Beach, which runs south from the town of Orleans into Chatham, South Beach achieved its own identity in January 1987 when a severe winter storm broke through the barrier beach directly east of Chatham Light, creating a broad inlet that remains today. Initially an island, the northern tip of the beach soon re-connected to the mainland just south of Chatham Light, making it accessible by foot. The southern end of the spit has been expanding steadily southward, growing by well over a mile since the 1987 break, so that the beach now measures about five miles in length. In November of 2006, the southern tip of the beach connected to the north end of South Monomoy, creating a land bridge from Chatham Light to Monomoy Light.

Most of South Beach is composed of dune habitats, sparsely vegetated with beach grass (Ammophila) and a few stunted shrubs (mostly bayberry). Additionally – and most significantly – extensive tidal flats are present on the west (inner) side of the beach, particularly along the southern third or so. Increasingly, the inner portions of the flats are developing into patches of salt marsh vegetated with Cord Grass (Spartina alterniflora).

Local birders continue to watch this geological metamorphosis with great interest, eager to see how the area's abundant avifauna adapts to the inexorable changes in this dynamic and ephemeral corner of the world. Free of vehicle traffic since the 1987 break, the beach still attracts considerable boat and foot traffic during the summer, but, for the most part – and especially in comparison to other such areas on Cape Cod – remains largely undisturbed and pristine. The avifauna has responded to this seclusion and the expanding, food-rich flats. The concentrations of shorebirds, terns, gulls, and seabirds are among the most impressive anywhere in the Northeast, typically exceeding those found even on South Beach's renowned neighbor to the west, Monomoy.