As a pigtailed macaque troop moved towards the railway track, I got curious. Will they cross it today? I have never seen them moving across it. One by one, all of them assembled on the trees lining the railway track. A sub-adult male cautiously descended down and, within a blink of an eye, crossed the track and climbed another tree on the other side. Two juveniles and one adult female followed him. As an adult male tried to join them, he paused. The sharp whistle of an approaching train forced him to retreat to his previous position. Panic and chaos ran through the troop as the train came close. And when it passed them with its ear-splitting whistle the troop dispersed helter-skelter and ran towards the forest leaving half the troop on the other side of the track. That night, perhaps not for the first time, the troop slept divided, on either side of the track, something they would never do otherwise, and it was perhaps not the last time they would have to do it.
A death trap…
This railway track is an important one that connects several important commercial towns of upper Assam (Dibrugarh, Tinsukia, Digboi and Duliajan) to Guwahati and the rest of India. It was laid down during the 1930s basically to streamline the transportation of tea, coal, oil and important timbers from upper Assam to Guwahati. In this process the Hollongapar Gibbon Wildlife Sanctuary became fragmented into two unequal chunks of forests. In addition to scores of other problems, this track has always posed a major threat to the wildlife of this isolated and fragmented 20.98 km2 sanctuary, most popularly known for its staggering primate community and possibly one of the highest primate density areas in the world.
During one of the field-days, when I was venturing into the forest, I saw a troop of capped langurs feeding on the ripe fruits of Hoanlu (Litsea monopetala), a few of them on the tree and the rest on the ground along the railway line. On my way back in the evening, I hit upon something on the track. It was the carcass of a sub-adult capped langur, one of the members of the same troop that I saw feeding in the morning. This unfortunate individual probably forgot that speed is not its forte while on the ground.
For primates like the arboreal hoolock gibbon, which never descends to the forest floor, this track is an extreme barrier. There are three groups of hoolock gibbons, consisting of 11 individuals, which have been trapped in the smaller forest chunk of about 2 km2 (Compartment 1, as it is administratively known) of the sanctuary. Assuming that the population was trapped after the construction of railway line (in the 1930s) and the fact that the patch was already dismembered from the contiguous forest at the time of the construction, the gibbons are probably fighting their battle of survival in the patch for last 80 years!
Amongst the other primates, the most terrestrial stump-tailed macaque and possibly the nocturnal slow loris never cross this track; this means that the resources readily available across the railway track always remains inaccessible to them. Only the rhesus macaque, owing to its mastery over ‘terrestrial matters’ is able to manage this deadly trap and a herd of 30-40 residential elephants perhaps! This herd crosses this track almost on a regular basis. Although it is heartening to know that no elephant death has ever been reported here, the credit for this must go to the elephant’s instincts, honed over million years of evolution, rather than to the lethargic forest department or the mindless train drivers for whom speed is too much to resist even as the track is dotted with elephant corridor signboards.
Besides these conspicuous and so-called ‘enigmatic’ animals, whose deaths invariably make news, there are numerous reptiles, amphibians and insects whose deaths go completely unnoticed, unannounced, forgotten. Even a causal walk along the track and you stumble upon the disfigured remains of hundreds of animal bodies scattered all around.
Besides the railway track, a road that runs through the sanctuary is another threat taking its toll on the wildlife of the sanctuary. This three kilometer road connects four villages adjacent to the sanctuary with the neighbouring Mariani town clogged with vehicles throughout the day. Recently this ‘deplorable’ road was repaired and was given a facelift to make it much ‘smoother’. It’s extremely agonizing to watch the reckless drivers testing their driving skills on it at a breakneck speed. The canopy above the road is wide open and it is frequently observed that arboreal primates and squirrels struggle to cross this gap. For reptiles and amphibians, crossing this gap of forest is not that an easy task, many lost their life in such attempts.
Roads, railways and other linear infrastructures have made a pervasive incursion in most of the forest causing mortality of wildlife, severely disrupting animal movement, reduce the amount and quality of habitat and increase the risk of local extinction. The effect of these structures on the wildlife in some cases is glaring whereas in many it is very subtle.
To mitigate the problem of road kill and increase the permeability of roads to wildlife, management agencies and conservation organization are seeking engineering solutions. There is now an increasing use of rope bridge overpasses and various underpasses in providing connectivity to rainforest fauna worldwide.
Taking cue from such practices, the Assam Forest Department has been trying to construct two overpasses across the track in collaboration with the railways. Two steel ropes (wrapped in green plastic cover) were thus laid down over the track thus connecting two compartments. It was of course expected that the gibbons would use them and life would be fine again. It, however, just didn’t work. Nobody knows why or has made the effort to find out why. Probably the steel ropes were too artificial a lure for them. Now there is a plan to construct a full-fledged bridge over the tracks. Will this work? Nobody, of course, knows.
A similar effort was attempted in the Borajan fragment of the Bherjan-Borajan-Podumoni Wildlife Sanctuary in Assam with limited success. Canopy bridges of bamboo poles were placed in the canopy openings inside the forest. Interestingly, hoolock gibbons, capped langurs and Assamese macaques have used these canopy bridges whereas the pigtailed and rhesus macaques have never.
The feasibility of using bamboo as bridges on the long run is questionable owing to the fragile nature of the bamboo, which tends to decay over time and become a liability rather than a solution. However, it must be recognized that natural connections rather than artificial structures are more likely to be preferred by rainforest species.
The problem of roadkills is not going to go away any time soon. We need this important infrastructure for it brings with it development but we also need wildlife to be free from this threat. Our prime concern should be never to plan for roads that run through important wildlife habitats and divert the existing ones whenever possible. Even if cannot do so much, we should modify their use in certain ways, as for example, banning their use at times when roadkills are most likely. The importance of such measures for conservation and wildlife management is invaluable.