Upper Dihing (West) Complex

Year of compilation: 2004

Site description (baseline)
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.

Pressure/threats to key biodiversity
MAIN THREATS: Encroachment by forest villagers; Encroachment by fringe villagers; Pollution from oil and coal mining; Expansion of oil and coal mining; Illegal felling of trees; Illegal fishing; Poaching; Snaring and collection of eggs and ducklings; Use of pesticides in the nearby tea gardens.

The main issue is mining of oil and coal, the former is restricted to Upper Dihing (West Block) RF, the latter in Joypur and Dilli RFs. Many of the water bodies near oilrigs are heavily polluted, thus posing serious threat to the environment. Coal mining in Joypur is done illegally. This needs to be stopped at once. These forests, especially Upper Dihing (West Block) RF were logged since 1930s which was a major source of raw material for plywood industries and trolley line was laid inside the forest, but that is now abandoned. Despite heavy logging, the habitat and wildlife survived to a great extent. Illegal felling of trees, encroachment by forest villagers and poaching, including collection of eggs and ducklings, of the White-winged Duck are other major issues. After the great earthquake of 1950 and subsequent floods, many displaced persons were settled inside Upper Dihing (WB) RF as ‘Forest Villagers’. This short-term solution led to some of the finest habitats of the White-winged Duck, Masked Finfoot and Elephant being cleared for settlement because of their suitability for paddy cultivation (marshy area with pools). Lakkhipathar, Borjan, Balijan are some such examples. Unfortunately, not much can be done now, except for protecting the remaining habitat from further encroachment and degradation.

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

Recommended citation
BirdLife International (2023) Important Bird Area factsheet: Upper Dihing (West) Complex. Downloaded from on 01/06/2023.