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Location India, Assam
Central coordinates 95o 28.50' East  27o 16.00' North
IBA criteria A1, A2
Area 46,775 ha
Altitude 120 - 474m
Year of IBA assessment 2004

Bombay Natural History Society

Site description This complex includes six Reserve Forests and three proposed Reserve Forests, all contiguous with each other. The areas constituting this IBA are Upper Dihing (27,500 ha), Joypur (10,870 ha), Dirak including additions (3,708 ha), Dilli (3,030 ha), Makumpani including additions (538 ha), Desali (200 ha), Digboiwest block (929 ha). Together they form the largest contiguous tropical rainforest area extant in the whole of Brahmaputra Valley (Choudhury 1996a). Of these, the Upper Dihing (West Block) has a long history of protection and management as a Reserve Forest, which was notified more than a century ago, in 1888. Some of the finest rain forests on flat plains in India are seen here. The area varies from slightly undulating plains in Upper Dihing to hills in Joypur, Dirak and Dilli, which are the foothills of the Patkai Range. The habitats in Dilli, Joypur and Dirak are contiguous with the forests of Arunachal Pradesh. Burhi-Dihing is the main river flowing through the site. Other notable rivers are Disang or Dilli, Dirak, Namsang and Digboi. Many small perennial streams criss-cross the area, noteworthy are the Janglu and Pawoi nullahs. These forests, especially Upper Dihing (West Block) have the largest known population of the globally endangered White-winged Duck Cairina scutulata (Choudhury 1996a, 1998). Together with other forests, the estimated population is higher than in any IBA in the world (BirdLife International 2001, Choudhury 2000). This area is also rich in primates and was recommended for protected area status way back in the 1980s (Choudhury 1989). Five species of hornbills occur in the area, including the rarer Brown Hornbill Anorrhinus tickelli and the Rufous-necked Hornbill Aceros nipalensis. Soraipung (meaning ‘bird spring’) in Upper Dihing is a well-known site for the Asian Elephant Elephas maximus and avifauna. The habitat is Tropical Rainforest. Champion and Seth (1968) described it as ‘Assam Valley Tropical Wet Evergreen Forest’. Arundo donax, Imperata cylindrica and Saccharum spp. occur in the scattered swampy/marshy depressions.

Key Biodiversity 

AVIFAUNA: More than 300 bird species have been recorded so far, probably more are present as many skulking and dense forest birds are difficult to see (A. U. Choudhury pers. comm. 2002). In the 1870s, the White-winged Duck was common in Tinsukia and Dibrugarh districts (Hume and Marshall 1879-1881; Baker 1908) and it was considered to be the fourth commonest duck species (after Teal Anas crecca, Mallard A. platyrhynchos and Gadwall A. strepera) at forest beels/ jungle pools/ wetlands throughout the Sadiya Frontier Tracts in the 1930s, with at least a pair in almost every waterlogged area (Parsons 1939, BirdLife International 2001). Most of the White-winged Ducks were reported from this IBA site during a study carried out by Choudhury in 1992-96. The population was estimated to be 90 in the Upper Dihing RF (West Block) alone, 19 in Joypur RF during 1992-94 (Choudhury 2000). Lone birds or in small groups such as in twos and threes can easily be seen in the secluded jungle pools of Upper Dihing (West Block) RF. The Upper Dihing (West Block) RF is also a good place for other rare birds such as Rufous-necked Hornbill Aceros nipalensis, Beautiful Nuthatch Sitta formosa, Brown Hornbill Anorrhinus tickelli and White-bellied Heron Ardea insignis. Perhaps this is the only IBA site in Assam, where the Beautiful Nuthatch can be seen (Mridu Paban Phukan verbally to Kulojyoti Lahkar) as there is no recent report of this species from anywhere in Assam (Choudhury 2000), except Barail Hills (Alström et al. 1994). The elusive White-bellied Heron Ardea insignis can also be seen in Joypur Reserve Forest particularly in winter. Usually singles and twos are seen on the bank of Namsang and Burhi Dihing rivers (Mridu Paban Phukan verbally to Kulojyoti Lahkar). Another rare bird the Pale-capped Pigeon Columba punicea was also sighted in this IBA, in all three reserve forests. In this IBA, sighting of Rufous-necked Hornbill is also not uncommon as small groups of this globally Vulnerable species is seen deep inside the forest.

OTHER KEY FAUNA: The area is rich in other wildlife, with six species of primates: Hoolock Gibbon Hylobates hoolock, Capped Langur Trachypithecus pileatus, Pig-tailed Macaque Macaca nemestrina, Rhesus Macaque M. mulatta, Stump-tailed macaque M. arctoides, Assamese Macaque M. assamensis Slow Loris Nycticebus coucang (Choudhury 1996b) and two large cats Tiger Panthera tigris and Leopard P. pardus. The Clouded Leopard Neofelis nebulosa, Leopard Cat Prionailurus bengalensis, Marbled Cat Pardofelis marmorata and Golden Cat Catopuma temminckii probably exist, though records are lacking. The Wild Dog Cuon alpinus is another predator of these forests. Their main prey species are Sambar Cervus unicolor and Barking Deer Muntiacus muntjak. Asian Elephant and Gaur Bos frontalis are two large mammals. The closed canopy forest provides habitat to Malayan Giant Squirrel Ratufa bicolor and Common Giant Flying Squirrel Petaurista petaurista (Choudhury 1996a). Not much is known about the reptiles and amphibians.

Populations of IBA trigger species

Species Season Period Population estimate Quality of estimate IBA Criteria IUCN Category
White-winged Duck Asarcornis scutulata resident  2004  present  A1  Endangered 
Lesser Adjutant Leptoptilos javanicus resident  2004  present  A1  Vulnerable 
White-bellied Heron Ardea insignis resident  2004  present  A1  Critically 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 
Pale-capped Pigeon Columba punicea resident  2004  present  A1  Vulnerable 
Rufous-necked Hornbill Aceros nipalensis resident  2004  present  A1  Vulnerable 
Yellow-vented Warbler Phylloscopus cantator resident  2004  present  A2  Least Concern 
Beautiful Nuthatch Sitta formosa resident  2004  present  A1  Vulnerable 

IBA Monitoring

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

Agriculture and aquaculture annual & perennial non-timber crops - small-holder farming happening now some of area/population (10-49%) very rapid to severe deterioration high
Biological resource use fishing & harvesting aquatic resources - unintentional effects: subsistence/small scale happening now small area/few individuals (<10%) slow but significant deterioration low
Biological resource use hunting & collecting terrestrial animals - intentional use (species being assessed is the target) happening now some of area/population (10-49%) very rapid to severe deterioration high
Biological resource use logging & wood harvesting - unintentional effects: subsistence/small scale happening now small area/few individuals (<10%) moderate to rapid deterioration low
Energy production and mining mining and quarrying happening now small area/few individuals (<10%) very rapid to severe deterioration low
Energy production and mining oil and gas drilling happening now small area/few individuals (<10%) very rapid to severe deterioration low
Pollution agricultural & forestry effluents - herbicides and pesticides happening now small area/few individuals (<10%) slow but significant deterioration low
Pollution industrial & military effluents - seepage from mining happening now small area/few individuals (<10%) very rapid to severe deterioration low
Residential and commercial development housing and urban areas happening now small area/few individuals (<10%) very rapid to severe deterioration low


IUCN habitat Habitat detail Extent (% of site)
Forest   -
Wetlands (inland)   -
Artificial - terrestrial   -

Land use

Land-use Extent (% of site)
agriculture -
Notes: Agriculture
forestry -
Notes: Forest
urban/industrial/transport -
Notes: Industry (oil installations)

Acknowledgements Key contributors: Anwaruddin Choudhury, Kulojyoti Lahkar and Mridu Paban Phukan.


Alstrom, P., Jirle, E., Jaderblad, M., Kjellen, N., Larsson, G., Paulsrud, A., Saellstrom, J., Smitterberg, P. and Alind, P. (1994) Birds and Mammals observed in Assam in Feb. 1994. Unpublish report.

Baker, E. C. S. (1908) The Indian Ducks and their Allies. First edition. Bombay Natural History Society/ R.H.Parker, London. xi + Pg 292.

BirdLife International (2001) Threatened Birds of Asia: The BirdLife International Red Data Book. BirdLife International, Cambridge, U.K.

Champion, H. G. and Seth, S. K. (1968) A revised survey of forest types of India, Govt. of India Press, Delhi.

Choudhury, A. U. (1989) The Primates of Assam, their distribution, habitat and status. Unpublished Ph.D. thesis, Gauhati University. Pp. 300 + maps.

Choudhury, A. U. (1996a) Survey of the White-winged Wood Duck and Bengal Florican in Tinsukia district and adjacent areas of Assam and Arunachal Pradesh. The Rhino Foundation for Nature in NE India. Guwahati.

Choudhury, A. U. (1996b) Survey of primates in some parts of eastern and central Assam. Final Report to ASTEC, Guwahati. 32pp. + maps.

Choudhury, A. U. (1998) Status and conservation of the white-winged duck in eastern Assam, India. OBC Bulletin 28: 14-17.

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

Hume, A. O. and Marshall, C. H. T. (1879-1881) The game birds of India, Burmah and Ceylon- 3 Vols. Authors, Calcutta.

Lahkar, K. (2001) Birds of Upper Dihing (East Block) and Kakojan Reserved Forests and Digboi Forest Area Report to the Bombay Natural History Society, Mumbai. (Unpubl.) 30pp. + 1 map.

Parsons, R. E. (1939) Migration routes of Geese. J. Bombay Nat. Hist. Soc. 40(4): 764-765.

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Recommended citation  BirdLife International (2016) Important Bird and Biodiversity Area factsheet: Upper Dihing (West) Complex. Downloaded from on 28/10/2016

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