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Location India, Assam
Central coordinates 94o 38.00' East  26o 59.00' North
IBA criteria A1, A4i
Area 150 ha
Altitude 0
Year of IBA assessment 2004

Bombay Natural History Society

Site description This IBA site includes three large historic tanks Joysagar (60 ha), Sivasagar (50 ha) and Gourisagar (40 ha) and their high banks in and around Sibsagar town in eastern Assam. Since time immemorial, birds have been protected in these sacred temple tanks. Every winter hundreds, often thousands, of ducks and geese spend the whole day resting and feeding on these tanks, which are easily accessible by metalled roads. The surrounding terrain is flat plain country. Sibsagar and Joysagar tanks are known for their spectacular flocks of ducks and geese. The largest wintering flocks of Bar-headed Anser indicus and Greylag Anser anser geese ever recorded in Assam, were in Joysagar tank. About 5,800 and 3,000 respectively were counted in 1995 (Bibhab Talukdar in Choudhury 2000). Most of the tanks are open water but on the margins there is emergent and floating vegetation. Fortunately, these tanks are free from Water Hyacinth Eichhornia crassipes.

Key Biodiversity 

AVIFAUNA: More than 60 species of birds have been recorded on the waterspread as well as in the trees on the banks. Lesser Adjutant Leptoptilos javanicus and Greater Adjutant L. dubius are seen in the trees growing around the tanks. Choudhury (1988) has seen seven Baer’s Pochard Aythya baeri on Sibsagar tank in 1988, amongst thousands of other ducks. Great Crested Grebe Podiceps cristatus, is seen in Sibsagar and Joysagar tanks, sometimes in hundreds. Before return migration, they appear in breeding plumage and territorial display is seen. Both the Bar-headed and Grey geese are present in large numbers, much above their 1% biogeographic population threshold, as recently determined by Wetlands International (2002). For example, between 52,000 to 60,000 Bar-headed Goose are estimated in the world, with 1% population threshold of 560. It is not uncommon to see 1-2 thousands in these tanks. In 1995, a total of 5,800 were counted, which constitute about 10% of the population. Similarly, the South Asian non-breeding population of the Greylag Goose Anser anser rubirostris is estimated to be 15,000 (Wetlands International 2002). With a total of 3,000 found in these tanks in 1995, it constitutes nearly 20% of this biogeographic population. Thus, this site easily qualifies A4i criteria.

OTHER KEY FAUNA: As these tanks are surrounded by human habitation, no large wild mammal is present. Only Smooth Indian Otter Lutrogale perspicillata occasionally fish in the tanks, but they are now extremely rare. Among reptiles, large softshell turtles have been recorded.

Populations of IBA trigger species

Species Season Period Population estimate Quality of estimate IBA Criteria IUCN Category
Baer's Pochard Aythya baeri winter  2004  present  A1  Critically Endangered 
Greylag Goose Anser anser 2004  present  A4i  Least Concern 
Bar-headed Goose Anser indicus 2004  present  A4i  Least Concern 
Lesser Adjutant Leptoptilos javanicus resident  2004  present  A1  Vulnerable 
Greater Adjutant Leptoptilos dubius breeding  2004  present  A1  Endangered 
White-rumped Vulture Gyps bengalensis non-breeding  2004  present  A1  Critically Endangered 
Slender-billed Vulture Gyps tenuirostris non-breeding  2004  present  A1  Critically Endangered 

IBA Monitoring

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

Biological resource use hunting & collecting terrestrial animals - intentional use (species being assessed is the target) happening now small area/few individuals (<10%) moderate to rapid deterioration low
Human intrusions and disturbance work and other activities happening now small area/few individuals (<10%) slow but significant deterioration low
Residential and commercial development housing and urban areas likely in long term (beyond 4 years) small area/few individuals (<10%) very rapid to severe deterioration low


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

Land use

Land-use Extent (% of site)
urban/industrial/transport -
Notes: Human habitation
water management -
Notes: Wetland

Acknowledgements Key contributors: Diptimanta Barooh, Anwaruddin Choudhury and Kulojyoti Lahkar.


Choudhury, A. U. (1988) Some rare ornithological records from Sibsagar, Assam. Cheetal 29(2): 3- 9.

Choudhury, A. U. (1991) Bird observations from Sibsagar District, Assam, India. Forktail 6: 35-42.

Choudhury, A. U. (2000) The Birds of Assam. Gibbon Books & WWFIndia NE Region, Guwahati. Pp. 240.

Wetlands International (2002) Waterbird 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: Sibsagar Tanks. Downloaded from on 25/10/2016

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