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Kaliveli Tank is a semi-permanent, fresh to brackish water lagoon, which empties into the sea through a narrow channel connecting the tank with the Yedayanthittu Estuary to the northeast. The water level in the tank fluctuates according to precipitation; the tank reaches its maximum extent at the end of the Northeast Monsoon, and in years of low rainfall, dries out completely for a few months during the summer. At such times, the encroachment of paddy fields reduces the size of the tank by as much as one third. The average depth of water at the end of the monsoon is about 1 m, and the maximum after heavy rainfall, about 2 m. By the end of the monsoon, the lagoon is normally full of fresh water, from the run-off from neighbouring farmland. Subsequently, as the inflow of fresh water diminishes, there is some inflow of seawater from the estuary, and the lagoon becomes brackish, particularly at its northern end. The lagoon is occasionally flooded by seawater during cyclonic disturbances (Scott 1989). Yedayanthittu estuary lies about 3 km to the northeast of the tank. This estuary has large areas of inter-tidal mudflats, but only tiny relicts of the once extensive mangrove forests now remain. There are some 500 ha of saltpans alongside the estuary immediately to the north of the Marakkanam road bridge across the channel from Kaliveli Tank. Until about 25 years ago, the entire region was heavily forested, but almost all the forest has been cleared, and the tank and estuary are now surrounded by cultivation and scrubby thorn woodland. There are some low sand dunes by the channel linking the tank to the estuary. The Kaliveli watershed extends from Auroville Plateau south for about 30 km and has an area of approximately 25,000 ha (Scott 1989). These sites have a wide variety of sedges and grasses, interspersed with barren sandy areas and muddy margins. As the lake fills with fresh water in November, numerous aquatic plants germinate. Amongst the many species of algae in the brackish areas, Enteromorpha intestinalis is particularly common. There are extensive reed beds and sedges in the less saline areas. A few straggly mangrove bushes are all that remain of what must once have been a large mangrove forest (Pieter 1987). The wetlands are situated amidst agricultural land and arid thorn scrub.
AVIFAUNA: The Tank and the estuary are extremely important staging and wintering areas for a wide variety of migratory waterfowl (Pieter 1987, Scott 1989). Pieter (1987) has recorded 105 species of water and land birds, while Perennou (1987) noted 78 species of waterfowl, including 13 species of Anatidae and 30 species of shorebirds. The area regularly holds over 30,000 ducks in winter; and 20,000-40,000 shorebirds and 20,000-50,000 terns during the migration period. Pieter (1987) noted about 40,000 birds in the Tank, and another 20,000 in the estuary. Although the number of species is consistent during this period, the species populations do fluctuate. It is assumed that there is a continuous movement of various species between Point Calimere, Vedanthangal (both IBAs) and the Kaliveli Tank (Pieter 1987). In March and April, as the water level recedes, the lagoon attracts large congregations of pelicans, herons, egrets, storks and ibises. Spot-billed Pelican Pelecanus philippensis is a regular visitor in flocks of 30-200 individuals, and Greater Flamingo Phoenicopterus ruber sometimes occurs in very large numbers. The first flock of Greater Flamingo usually arrives in late November or early December, and numbers build up to a peak of 6,000-7,000 in March and April. In 1987-88, 200 Spotbilled Pelican (1% threshold is 40: Wetlands International 2002), 50,000 shorebirds, 30 Ruddy Shelduck Tadorna ferruginea, 1,000 Asian Openbill Anastomus oscitans, 3,500 Red-crested Pochard Netta rufina, and some shorebirds like Little Stint Calidris minuta (4,000-5,000; 1% threshold is 2,000: Wetlands International, 2002), Curlew Sandpiper Calidris ferruginea (350), Lesser Sand Plover Charadrius mongolus: (280) were reported by Scott (1989). Perennou (1989) found three Greater Spotted Eagle Aquila clanga spending the whole winter in 1986-87 in Kaliveli. Their present status is not known. This site easily qualifies A4i (1% of biogeographic population) and A4iii (= 20,000 waterbirds) criteria. By the presence of globally threatened and many Near Threatened species, it also qualifies A1 (Threatened Species) criteria.
OTHER KEY FAUNA: The area was formerly heavily forested but now only fragments remain. An 18th century stone inscription found close to the tank showed a king hunting elephants in the surrounding forests! Now, only a few Golden Jackal Canis aureus and Black-naped Hare Lepus nigricollis remain.
BirdLife International (2020) Important Bird Areas factsheet: Kaliveli Tank and Yeduyanthittu estuary. Downloaded from http://www.birdlife.org on 15/07/2020.