An eastern hoolock gibbon. A Telegraph picture

Guwahati, May 12: Assam’s primate diversity has now become richer with the sighting of eastern hoolock gibbons (Hoolock leuconedys) in Sadiya subdivision in Tinsukia district — marking the reserve forest as a potential conservation site for the species.

This is the first time that this species has been sighted in the state. A survey team, led by Aaranyak’s primatologist Dilip Chetry, stumbled upon the species in three reserved forests of Sadiya subdivision.

Before the hoolock gibbon survey was undertaken, the Northeast was known to harbour 11 of the 25 species of these primates present in the country. Of these 11, nine were found in Assam. Now the number stands at 10. The survey was carried out from March to May. A total of 23 groups of eastern hoolock gibbons were sighted.

The eastern hoolock gibbon is from the Hylobatidae (gibbon) family. The species is found in Myanmar, east of the Chindwin river, and in south west Yunnan province of China.

“The survey team not only sighted the eastern hoolock gibbons but also subsequently identified the species on the basis of scientific observations and research. The colour differences, which distinguish it from the western hoolock gibbons, were confirmed through binoculars and photographs. Their identity was further authenticated by reviewing recent literature and personal correspondence with primate taxonomist Colin P. Groves,” Chetry said today.

The primary distinguishing characteristic of the eastern species from their western counterparts is that their limbs are lighter in colour than their body coats.

Chetry said though the gibbon survey covered six reserve forests of Sadiya range, the eastern hoolock gibbon was spotted only in three reserve forests — Hallow gaon, Kukuramara and Kundil Kolia. Unfortunately, the survey confirmed the harsh reality that the gibbon population has been wiped out from the other three reserve forests — Deopani, Sadiya Station North Block and Sadiya Station West Block.

“The sighting of the eastern hoolock gibbon has added to the state’s primate diversity. It means that Assam now has 10 species of non-human primates and this is the highest diversity of primates in any state of the country,” Chetry said.

The study has marked Kundi Kolia reserve forest as a potential conservation site for the species. This being the sole population of the species in Assam, the Kundil Kolia reserve forest can now be upgraded to a wildlife sanctuary under the name of Kundil Kolia wildlife sanctuary for conservation of the rare eastern hoolock gibbon in the state.

Last year, eastern hoolock gibbons were sighted in Mehao wildlife sanctuary in Arunachal Pradesh. Around 150 groups of the species were recorded there. The survey also recorded forest loss and fragmentation because of agricultural expansion (ginger and mustard cultivation), encroachment by human settlement and illegal felling of trees. These have been identified as the most discernible factors, posing a grave threat to the survival of gibbons in this area. The study team also noted that the manpower of the forest department in Sadiya Range was grossly inadequate. Only eight forest personnel patrol the entire forest cover of the sub-division and there are no camps inside the forest area.