The coastline of Saba is mostly rubble and rocky cliffs that are or taller with no permanent beaches. The steep terrain and sheer bluffs dropping almost straight down to the ocean's edge prevents the formation of mangrove swamps or much vegetation. There are eight bays tucked into the cliffs around the island; Cove Bay, Spring Bay, Core Gut Bay, Fort Bay (location of the island's only port), Tent Bay, Ladder Bay, Wells Bay and Cave of Rum Bay. The shoreline of the island is of particular value to sea birds, and has been designated an Important Bird Area (IBA AN006 - "Saba Coastline") by BirdLife International. Saba is home to about sixty species of birds, many of which are sea birds that use the holes and crevices of the steep cliffs and two small islands for breeding and feed in the waters around the island. Saba's shoreline is home to the Caribbean's largest breeding colony of Red-billed tropicbird ("Phaethon aethereus"). The Audubon's Shearwater ("Puffinus lherminieri") is another common bird, and is the national bird of Saba as well as being featured on their coat of arms.