Feasts, Famines and a Tale of Two Primates
June 2011: I countered the chill of an early rainforest morning by walking briskly along the damp forest trail towards where I had left my study group of lion-tailed macaques (LTM) Macaca silenus the previous night. The shrill cackle of the Grey Jungle Fowl Gallus sonneratii stridently called the denizens of the day to wakefulness.
Nilgiri langurs Trachypithecus johnii whooped their early morning communiqué across the still dark canopy and from deep within the wet undergrowth, a Malabar Whistling Thrush Myophonus horsfieldii called melodiously. Tall trees, swathed in the mist of the disappearing night, reached towards the melting darkness above, like sentinels of mystery. At first light, I reached the location where my study-group spent the night after their last major meal for the day. The group usually rested close to where they fed at dusk and although I couldn’t see their dark forms in the dimness, I could hear the characteristic, soft ‘coo’ of monkeys calling to each other. Soon, small dark forms emerged from the dense foliage above, magical figures in silky black with long white manes highlighting their expressive faces.
THE SILENT VALLEY NATIONAL PARK
I was in the verdant rainforests of the Silent Valley National Park in the Palakkad district of north Kerala, to study how LTMs coped with seasonal changes in fruit availability. Ranging from 800 to 2,383 m. (Anguinda peak), Silent Valley comprises 90 sq. km. of luxuriant mid-elevation rainforest and high-elevation grassland-shola complexes, is contiguous with the Mukurti National Park, and rises sharply to meet the Nilgiris in the north. The terrain is undulating with rolling forested hills interspersed with grasslands, rocky crags, steep cliff faces and shola forests nestled in the crooks. The river Kunthi waters this forest, flowing down from the high reaches of the Nilgiri plateau into the Mannarkad plains in the south.
OF FRUITS, FRUGIVORES AND RAINFORESTS
The LTM is an endangered primate, endemic to the rainforests of the Western Ghats. Studies have shown that most rainforests across the world undergo a seasonal scarcity of fruit during the driest months. During this pinch period, both the number of tree species bearing fruit and the total number of trees in fruit are at their lowest. Recent studies have demonstrated that the pattern is similar in the rainforests of the southern Western Ghats, January to early April being the lean period, and a tough time for fruit-eating animals. Presumably, life begins to improve for frugivores with the onset of the summer showers in March-April each year, following which many trees start fruiting. The LTM is an ‘obligate frugivore’, in other words although it eats seeds, flowers, nectar, some resins and insects, it relies upon mature fruits for a majority of its energy needs. I wanted to find out how an animal like the LTM, so dependent upon fruit, tides over this period of scarcity.
Animals often cope with low food availability by migrating to food-rich areas or by feeding on species they would normally give a miss. Some monkeys do indeed migrate but the ability of fruit-eaters to tide over lean periods also depends upon their physical ability to switch to certain foods including leaves and gums. Such adaptations evolved over millennia in response to resource scarcity. Some species in South America such as spider monkeys Ateles sp. and howler monkeys Alouatta sp. rely on green leaves, which are plentiful. Eating leaves, however, is dependent on the ability to digest toxins found in the leaves of most rainforest trees. Energy-rich gums, resins and other exudates from trees are more commonly consumed by smaller-bodied primates, which also require special digestive capabilities. Some small primates like the squirrel monkey Saimiri sciureus switch to insects during lean periods. But, searching for invertebrate food is time consuming and can be a staple food only for primates weighing less than four kilogrammes. The LTM has none of these choices, though it does consume insects.
IN SILENT VALLEY
So, what does a fruit specialist with very few choices do during hungry times? I expected the LTM to selectively track and feed on high-quality fruits in the lean season. With Dr. Ajith Kumar, one of India’s finest biologists as my guide, I honed in on Silent Valley, a prime (and celebrated) habitat for this rainforest specialist. The usual rigmarole with the Forest Department for permissions plus a long bumpy ride saw me at the guards’ quarters at Sairandhri section in the core area of the national park. I was offered a small room with a table and a rickety cot that was to be my home for the next few months. But I was happy. I was in Silent Valley!
My first task was to find an LTM group relatively close to camp, but the first few days brought trouble and despair. The monkeys seemed to elude me as I desperately looked for them, even a group that the forest guards said they frequently came across! And when I did find them, they just seemed to melt into the rainforest canopy. To top it all, I had one field assistant after another deserting me for fear of elephants and better economic prospects in nearby towns. But I persisted and it paid off. Within a fortnight I learned how to locate the LTMs by their calls. I would start my search for them when they were most vocal, early to mid-morning. My routine was to leave camp at first light, walk along the known trails and listen for the characteristic ‘coo’ calls the LTMs used to maintain group contact. Pretty soon, I was able to discern the different calls that the monkeys used and read tell-tale signs left behind by the group. Finding paths to traverse in search of the group also became much easier as I became familiar with my study area.
ON A MONKEY TRAIL
I was able to locate three troops within a radius of six kilometres, with one of them eventually becoming habituated to me. Once located, I would follow the group for as long as I could, sometimes all day until they retired for the night. But tracking monkeys was not exactly the most exciting occupation. Sometimes, it involved standing in the same place for hours, other times having to travel in fast bursts over undulating terrain. I frequently found myself scrambling over steep hills, sliding down slippery slopes, wading through streams and getting slashed by cane brakes and other intransigent undergrowth.
Initially the monkeys were wary and would retreat to the high canopy when they saw me. But they gradually got used to this figure always hanging around and staring up at them. Soon, curiosity got the better of many of the younger members and they would cautiously approach as close as five metres, examining me as closely as I was scrutinising them. One intrepid young male came within two metres, trying to intimidate the strange new primate with the signature upward head-jerk of his species!
Observing the daily activities of the LTM group, I became familiar with what they ate and how much time they spent doing different chores. Every 15 minutes, I would note the number of individuals, their age-sex class, and the activity of each individual. When they were feeding, I noted the type of food (plant or invertebrate) and the species and part (fruit, flower, nectar, seed, etc.) being eaten. After following the group for a few weeks, I was able to get an idea of their home range within which I determined the composition of tree species to understand food preferences, which food trees were more abundant and which were rare.
Soon, my botanical understanding of their home also grew better. I had to figure out which food trees were bearing fruits, flowers or seeds that the LTM fed upon and I eventually ended up monitoring the phenology of 195 trees of 15 major food species. This gave me an overview of seasonal variations in the food species available to the LTM. Additionally, I collected the fruits of species the group fed upon or that were established food sources. These I sun dried and analysed for nutritional content to see if there was any difference between them in the two seasons.
A RAINFOREST IN TWO SEASONS
After five months of pursuing monkeys over undulating terrain and measuring the diameter of trees, I returned to Bangalore. I immediately began to miss my days of rainforest monkey-watching. However, my study revealed some interesting results. Not surprisingly, there were fewer fruit-bearing trees between January and March and fruit availability increased after the onset of the pre-monsoon showers in late March. But, the new and exciting discovery was that the dry season fruits also happened to be nutritionally inferior to wet season fruits. What this essentially means is that fruit-eating animals in rainforests may not only face dry season food shortage, but also a drop in the quality of food, which compounds the severity of the lean period.
What did LTMs do when fruit was scarce? For one, the group travelled longer distances in search of specific high-quality foods, even when poor quality resources were more readily available. In the lean season I found these fruit specialists selectively tracking and consuming high-quality fruits of a tree called Drypetes wightii, found patchily distributed in clumps of six to eight trees. Although the LTMs did feed on Palaquium ellipticum which was three times more abundant than Drypetes wightii and found nearly everywhere, they would travel long distances to reach productive Drypetes patches. Nutritional analysis revealed that the nectar of Palaquium ellipticum fed upon by the LTMs, was much less nutritious when compared with Drypetes wightii fruits. In contrast, during the wet season when food was more plentiful, the group travelled less and seemed to choose from within trees of the same species. In this time of plenty, the LTMs fed predominantly on the seeds of Cullenia exarillata, the most abundant tree within their home range.
LIFE ON THE FOREST TRAIL
Although the LTM was the focus of my study, being in Silent Valley for five months gave me an opportunity to see a lot more of the life in this beautiful rainforest. I had many fascinating encounters. I watched a brown mongoose, oblivious to my presence, persistently search the leaf litter for its early morning meal. I spent many days under a gigantic fig tree Ficus nervosa, watching LTMs, Malabar giant squirrels Ratufa indica, Mountain Imperial Pigeons Ducula badia, Green Pigeons Treron phoenicoptera and a host of other birds feed off its massive fruit crop. I watched in breathless silence, as a muntjac Muntiacus muntjac approached ever so close. Slender neck moving in rhythm with its curious high-stepping gait, this shy animal that we usually see as a dashing blur of orange-brown, fed on the fallen figs, unaware of me as I hid behind a tree. My field assistant, on his way to join me for the day’s work, even sighted the rare and elusive Nilgiri marten Martes gwatkinsii close to camp.
I also had numerous sightings of the shy and nocturnal Indian chevrotain Moschiola indica dashing out in a flash of white-spotted black from perfect concealment in dense undergrowth or fallen logs. I had near brushes with Malabar pit vipers Trimeresurus malabaricus and large-scaled pit vipers Peltopelor macrolepis coiled green on green around the tip of a bush or blending in with the speckled brown of a flaking Mesua ferrea tree. I also discovered just how painful hornet stings could be. Bronzeback tree snakes Dendrelaphis tristis ‘leaping’ across branches, close encounters with foraging bears, run-ins with elephants along Silent Valley’s many streams and trails and discovering tiny frogs in waterholes in tree hollows were all part of the indelible experience. Tigers are rare sightings in rainforests so I was thrilled to stumble upon a tigress playing with her two little cubs less than 10 m. away. Needless to say, I had to beat a hasty retreat from the irked mother when she discovered my presence!
CONSERVATION AND RAINFOREST SCIENCE
The rainforests of the Western Ghats are an ancient entity and there is much to learn about their functioning. New species continue to be discovered here, even as the fascinating ecosystem and its resident wildlife are increasingly threatened by humans. Coffee, rubber and cocoa plantations continue making inroads into fragile rainforests and roads and mines hack through once-pristine landscapes in a seemingly unstoppable juggernaut of destruction. Hunting and forest produce extraction continue to be a problem in many areas. And on top of all this, we have climate change, which may alter flowering and fruiting patterns in rainforests, in turn affecting frugivorous animals. Studies in the rainforests of Amazon, Africa and Southeast Asia have revealed the complexities of rainforest ecology; the Western Ghats are no different and are governed by subtleties that must be unravelled by long-term scientific research. For, without understanding the ecological processes at work, we cannot possibly hope to design appropriate, science-based conservation strategies for these intriguing, and life-supporting ecosystems.
By Meghna Krishnadas