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Location India, Pondicherry,Tamil Nadu
Central coordinates 79o 44.22' East  11o 56.85' North
IBA criteria A4i, A4iii
Area 800 ha
Altitude 0
Year of IBA assessment 2004

Bombay Natural History Society

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.

Populations of IBA trigger species

Species Season Period Population estimate Quality of estimate IBA Criteria IUCN Category
Cotton Pygmy-goose Nettapus coromandelianus 2004  present  A4i  Least Concern 
Eurasian Wigeon Mareca penelope winter  2004  present  A4i  Least Concern 
Little Cormorant Microcarbo niger 2004  present  A4i  Least Concern 
A4iii Species group - waterbirds unknown  2004  20,000 individuals  unknown  A4iii   

IBA Monitoring

2003 very high not assessed not assessed
Good - based on reliable and complete / representative data

Agriculture and aquaculture livestock farming and ranching (includes forest grazing) - small-holder grazing, ranching or farming happening now small area/few individuals (<10%) slow but significant deterioration low
Biological resource use fishing & harvesting aquatic resources - unintentional effects: subsistence/small scale happening now some of area/population (10-49%) slow but significant deterioration medium
Biological resource use gathering terrestrial plants - unintentional effects (species being assessed is not the target) happening now small area/few individuals (<10%) no or imperceptible deterioration low
Biological resource use hunting & collecting terrestrial animals - intentional use (species being assessed is the target) happening now small area/few individuals (<10%) slow but significant deterioration low
Human intrusions and disturbance recreational activities likely in short term (within 4 years) some of area/population (10-49%) slow but significant deterioration medium
Invasive & other problematic species, genes & diseases invasive non-native/alien species/diseases - named species happening now majority/most of area/population (50-90%) slow but significant deterioration high
Pollution agricultural & forestry effluents - soil erosion, sedimentation happening now majority/most of area/population (50-90%) very rapid to severe deterioration very high
Residential and commercial development tourism and recreation areas likely in long term (beyond 4 years) some of area/population (10-49%) very rapid to severe deterioration medium


IUCN habitat Habitat detail Extent (% of site)
Artificial - aquatic   -

Land use

Land-use Extent (% of site)
fisheries/aquaculture -
Notes: Fisheries
urban/industrial/transport -
Notes: Transport
water management -
Notes: Water management

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


Ali, S. and Ripley, S. D. (1987) Compact Handbook of the Birds of India and Pakistan (Second Edition). Oxford University Press, Delhi.

Balachandran, S. and Alagahrajan, R. (1995) An ecological survey of the wetlands of Pondicherry with special reference to Ousteri lake. Institute of Restoration of Natural Environment, Nagercoil. Pp. 40.

Grimmett, R., Inskipp, C. and Inskipp, T. (1998) Birds of the Indian Subcontinent. Christopher Helm Ltd., London, U.K.

Jhunjhunwala, S. (1998) The ornithological importance of Ousteri lake and Bahour lake: A study of the habitat preferences of their waterfowl and waders. M.Sc. Dissertation. Salim Ali School of Ecology and Environmental Sciences, Pondicherry University.

Wetlands International (2002) Waterbirds Population Estimates: Third Edition. Wetlands International Global Series No. 12. Wageningen, the Netherlands.

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Recommended citation  BirdLife International (2016) Important Bird and Biodiversity Area factsheet: Ousteri Lake. Downloaded from on 24/10/2016

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