forests ecoregion covers most of the delta region, although the forests have mostly been cleared for agriculture and only small enclaves remain. Thick stands of tall grass, known as canebrakes, grow in wetter areas. The Sundarbans freshwater swamp forests ecoregion lies closer to the Bay of Bengal; this ecoregion is flooded with slightly brackish water during the dry season, and fresh water during the monsoon season. These forests, too, have been almost completely converted to intensive agriculture, with only of the protected. Where the delta meets the Bay of Bengal, Sundarbans mangroves form the world's largest mangrove ecoregion, covering an area of in a chain of 54 islands. They derive their name from the predominant mangrove species, Heritiera fomes, which are known locally as sundri or sundari. Animals in the delta include the Indian python (Python molurus), clouded leopard (Neofelis nebulosa), Indian elephant (Elephas maximus indicus) and crocodiles, which live in the Sundarbans. Approximately 1,020 endangered Bengal tigers (Panthera tigris tigris) are believed to inhabit the Sundarbans. The Ganges–Brahmaputra basin has tropical deciduous forests that yield valuable timber: sal, teak, and peepal trees are found in these areas. It is estimated that 30,000 chital (Axis axis) are in the Sundarbans part of the delta. Birds found in the delta include kingfishers, eagles, woodpeckers, the shalik (Acridotheres tristis), the swamp francolin (Francolinus gularis), and the doel (Copsychus saularis). Two species of dolphin can be found in the delta: the Irrawaddy dolphin (Orcaella brevirostris) and the Ganges river dolphin (Platanista gangetica gangetica). The Irrawaddy dolphin is an oceanic dolphin which enters the delta from the Bay of Bengal. The Ganges river dolphin is a true river dolphin, but is extremely rare and considered endangered. Trees found in the delta include sundari, garjan (Rhizophora spp.), bamboo, mangrove palm (Nypa fruticans), and mangrove date palm (Phoenix paludosa). Geology The Ganges Delta lies at the junction of three tectonic plates: the Indian Plate, the Eurasian Plate, and the Burma Plate. The edge of the Eocene paleoshelf runs approximately from Kolkata to the edge of the Shillong Plateau. The edge of the paleoshelf marks the transition from the thick continental crust in the northwest to the thin continental or oceanic crust in the southeast. The enormous sediment supply from the Himalayan collision has extended the delta about seaward since the Eocene. The sediment thickness southeast of the edge of the paleoshelf beneath the Ganges Delta can