Ousteri Lake

Country/territory: India

IBA Criteria met: A4i, A4iii (2004)
For more information about IBA criteria please click here

Area: 800 ha

Bombay Natural History Society
Most recent IBA monitoring assessment
Year of assessment Threat score (pressure) Condition score (state) Action score (response)
2003 very high not assessed not assessed
For more information about IBA monitoring please click here

Site description
Ousteri lake is located partly in Pondicherry and partly in Tamil Nadu near Ossudu village in the Villanur commune panchayat, about 12 km from Pondicherry, north of the Kaveri river. The lake depends on its catchment for 75% of its water, the rest comes from diversion channels. The lake is fed by local run-off and an intermittent river and has a bund on its western bank. It has an average depth of 1 m and dries up completely in summer. Besides being an internationally important site for migratory birds, the lake’s most valuable use is for irrigation. The lake has rich floral diversity of over 200 species of plants belonging to 60 families. Part of the bund is well protected by trees. It has extensive aquatic flora of the floating, submerged and emergent type.

Key biodiversity

AVIFAUNA: Ousteri is an important area for migratory waterfowl and regularly holds over 20,000 birds belonging to more than 40 species (Balachandran and Alagarrajan, 1995; Jhunjhunwala 1998). Balachandran and Alagarrajan (1995) have also conducted monthly surveys for a year. According to their census figures, many species occur much above their 1% threshold level, determined by Wetlands International (2002). For example, they have reported 10,500 Little Cormorant Phalacrocorax niger in June and 12,000 in August. According to Wetlands International (2002), the total number of Little Cormorant in South Asia is 150,000, which means that about 7% are found in Ousteri. Similarly, the number of Eurasian Wigeon Anas penelope can go up to 4,600 in February, while the 1% threshold is 2,500 (Wetlands International 2002). It means that nearly 2% of the biogeographic population congregate at Ousteri before migration. Information on the global population of the Cotton Pygmy Goose or Cotton Teal Nettapus coromandelianus is lacking (Wetlands International 2002) so we do not know the 1% population threshold. At Ousteri, Balachandran and Alagarrajan (1995) have noted up to 2,400 in June. This is one of the largest known congregations of this species in south India. The Cotton Pygmy Geese congregate here, as most of the wetlands dry up in summer, and large wetlands such as Ousteri have some water left. In India, Common Coot Fulica atra is resident in south India, while purely migratory in north India (Ali and Ripley 1987; Grimmett et al. 1998). In winter, the resident population is augmented by migratory birds from the temperate regions. This IBA is extremely important for the resident Coot population because when smaller wetlands are dry, Ousteri provides them refuge. In their one year monitoring of birds at Ousteri, Balachandran and Alagarrajan (1995) found that the maximum number of Coots, about 11,000, was found in the peak summer month of June. In July, the number came down to 9,000 as some birds probably moved to interior wetlands where rains had started, but the real change took place in August and September when 2,800 and 650 coots respectively were left. In winter months from October to February, the maximum number of Coots seen at Ousteri was 450. This further proves the importance of maintaining a chain of wetlands (IBAs), not only for rare species but also for such common species like the Coot. The Red Data Book species seen at Ousteri in 1994-95 are: Spotbilled Pelican Pelecanus philippensis (maximum of 6 seen in April 1994), Darter Anhinga melanogaster (maximum 2), Painted Stork Mycteria leucocephala (115 counted in September 1994), Eurasian Spoonbill Platalea leucorodia (only 6 seen in June 1994) and Black-headed Ibis or White Ibis Threskiornis melanocephala (up to 200 counted in June 1994) (Balachandran and Alagarrajan 1995.

OTHER KEY FAUNA: As this is basically a wetland surrounded by agricultural fields and human habitation, no mammal or reptile of conservation concern is found here.

Key contributors: Priya Davidar, Aju Mukhopaddhyay, Supriya Jhunjhunwala and S. Balachandran.

Recommended citation
BirdLife International (2022) Important Bird Areas factsheet: Ousteri Lake. Downloaded from on 11/08/2022.