UNESCO Biosphere Reserve; Strict Nature Reserve, Wildlife Refuges. One of the largest deltas in the world and characterized by a highly braided morphology, creating over 1,000 channels in the lower delta. The site covers the seaward edge, and is composed of extensive areas of open water, numerous islands, reedbeds, and other aquatic plants. 70% of the world catch of sturgeon come from the Volga tributaries, which are a vital link in the life cycle of other commercially important fish. During mild winters, the delta supports up to 750,000 waterbirds, including swans, geese and ducks, and summer molting ducks reach 400,000 individuals. Breeding wetland birds include the endangered pelican Pelecanus crispus; herons, Ardea cinerea; and egrets, Egretta alba (thousands of pairs each). The delta is a major staging area for many species of waterbirds, raptors and songbirds. The rise in the Caspian Sea level has caused a northward retreat of the foredelta.