Ganges Delta trees are found in these areas. The delta region has mangrove trees. 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
John Anderson (zoologist) and compared with "Orcaella fluminalis" and the Gangetic dolphin, "Plantanista gangetica". In 1875-6 he travelled to the same area under Colonel Horace Browne. This was cut short due to the murder of the consular officer Augustus Raymond Margary. Anderson made a third expedition for the Indian Museum in 1881–2 to the Mergui archipelago, Burma. Anderson made comparative studies of anatomy of the species that he collected. He worked on reptiles, birds as well as mammals such as of the genus "Hylomys". He also wrote on the ethnology of the Selungs of the Mergui archipelago. Many of the plant specimens that