Unlikely giants of the forest canopy

It was very windy that afternoon, the leaves and branches were flying, the skies were dark grey and a storm was imminent. It was summer and unbearably hot, so it was a welcome relief and pleasant to feel the strong wind. I was sitting under a tall Terminalia arjuna (Arjun) tree near the stream watching a giant squirrel’s nest.

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Suddenly, the squirrel which had been inside, came out of the nest and started wildly running up and down the tree trunk and leaping from branch to branch. I was flabbergasted and for some minutes, paused not knowing what to note down in my datasheet. What was this behavior and why was it doing this? It simply seemed to have no purpose at all.  For several minutes, I watched the squirrel rushing about madly and my bewilderment turned into amusement. And then, I thought to myself that the squirrel was playing. As ‘scientists’, we have been taught to observe and interpret animals as doing every thing with some purpose related to finding food, finding mates, resting or avoiding predators or some other ‘meaningful’ thing. We are also warned about not ‘anthropomorphizing’ when observing wild animals. But this squirrel was simply running up and down out of some kind of mad joy. Maybe it was nervous excitement at the approaching storm? After much dithering, I finally put down the behavior very firmly as play.  While play behavior has been noted in most mammal species, it is usually in a social context and as an interaction to which there is some seeming adaptive advantage. This other sort of crazy ‘play behavior’ before stormy weather has also been noted in some social species. But it was surprising to observe it in a solitary individual. And I wonder if there really is any adaptive explanation to such behavior.

The Malabar or the Indian giant squirrel is a handsome brightly colored arboreal squirrel found in the central Indian forests and in the Western Ghats. Among squirrels, these are the heaviest in India and they can weigh up to 2 kg. There is much geographical variation in its colour forms and several races/subspecies are recognized. It is active in the daytime, retiring to a nest it builds of twigs and leafy branches at dusk. Squirrel nests are also called dreys. It makes many such nests in its home range, and at any given time they can have up to 8-9 nests. These are mainly for sleeping in and changed periodically. It’s easy to figure out which nest is active at any point of time based on the ‘freshness’ of the leaves and the tightness of the structure. Old inactive nests are brown and loosely held together which may again be repaired and re-used. I have spent many hours watching these squirrels industriously build their homes. They put in a lot of thought into the construction as they would be careful to source their building material from elsewhere. They would never tear leafy branches from the tree on which they were building the nest. They would scamper off to neighbouring trees, selecting and breaking branches, making multiple trips back and forth. I had once seen the inside of a fallen nest and it was lined with soft cottony material – the fluffy balls of the silk cotton tree. While all squirrels use and build nests to sleep in, they also have special ‘nursery’ nests where the mother gives birth to pups and the pup shares the nest with the mother for many months, till it becomes independent.

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The busy squirrels are up at the crack of dawn to start off their foraging within their ranges which usually are around 1 to 2 hectares. Many a time, when I would start from our camp to begin my observations at 5-6 am in the morning while it was still dark, I would see a flying squirrel that lived near our camp retiring back into its cavity for the day, while its diurnal cousin, the giant squirrel would be coming out of its leafy nest. And every evening, I would stop my observations after seeing off the focal animal I was following into its nest and on the return to camp, come across the flying squirrel peeping out of its cavity. It was important for me to know which nest the squirrel had gone to sleep in, so that the next morning it would be easy to locate the individual.

I spent 6 months from December to May observing this species.  My study questions were about understanding their foraging and range use related to food availability patterns, therefore, I had to observe individuals. With most wild species, it is impossible to tell individuals apart unless they are marked or tagged. But with giant squirrels, there are ways to identify most individuals as they often may have one ear cut or bent due to frequent aggressive interactions during territorial fights, or some differences in facial markings or some quirky differences in the coloration/patterns of their long bushy tails. It was hard at first, and I lost a few animals I thought I could identify. But after a month, I managed to confidently identify five individuals that I could follow.  I followed 3 animals (an adult male, an adult female and a sub-adult male) in the disturbed habitat and 2 animals (an adult male and an adult male) in the undisturbed habitat. Both areas were in the riverine habitat. However, I ended up following the two individuals in the undisturbed habitat only in the initial winter months of my study, as I could not relocate them later in the season.

My work mainly involved following and watching these squirrels from dawn to dusk. I kept a continuous record of behaviors to understand their space-use patterns and time-budgets through the day. It was quite tiring and frustrating on some days when the focal squirrel would decide to make long sudden foraging movements into new areas in the deciduous forest away from its core area. But on most days, they remained in the core area which was among stands of Terminalia arjuna and Syzygium cumini (Jamun) near a perennial stream. And it was easy tracking them along this linear habitat.

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On some days in the week, I would do other work like laying grids in the areas used by the squirrels that I followed. This was done to map all the food trees, nest trees and other trees in their ranges and to determine their daily and overall ranges. I also tracked the phenology (leaf, flower and fruit) of all the trees in these grids twice a month to understand seasonal food availability patterns for the squirrels. I got used to constantly craning my neck up to look into the canopy in those days and at times when the squirrel would stay put in one place for a long time, it was a relief to sit or lie down while watching them up in the canopy with my binoculars.

It was a period of discovery, learning many little things each day just by watching their behaviour. One early morning, the squirrel whom I called Bent Ear was foraging on the unripe fruits of Terminalia bellerica (Behera) – tree squirrels are mainly seed predators and eat the hard seeds of many plant species. Then, it moved up the tree to the topmost leaves and started picking up the leaves and licking them. Initially I could not figure out what it was doing up there. Then it dawned on me that it was licking the dew-laden leaves for water. The langurs who shared the squirrels’ habitat also did the same thing. Another time, I watched a squirrel drinking water from a tree hollow.

I also learnt other random things. One day, some small brown pellets fell near me, while one landed in my hair. I was right below the squirrel and I realized that it was squirrel poop! Neat small cylindrical pellets, and hard with a distinctive smell.

I observed scent-marking and vocalizations that were used to advertise and mark territories. Giant squirrels have very distinctive alarm calls – remarkably loud rat-a-tat machine-gunning staccato calls. Another lesser known call I learnt was a contact call made while on the move through the canopy. This was a soft clicking call.  As if to let all the other tree creatures know it was coming and that the path should be clear.

The seasonal shifts in food availability along the stream meant that each day I came to know about different food items that squirrels ate. Over the six months, I recorded around 22 species in the diet with the main food being the seeds of Terminalia arjuna and Terminalia bellerica. And Bridelia retusa and the unripe fruits/seeds of Mangifera indica (Aam). In the summer, they would enjoy the unripe fruits of Aegle marmelos (Bael) and make a complete mess while eating the pulp. Barely able to grasp the large round fruit in their small paws, they would bite the outer rind with their strong incisors and scoop out the flesh and eat it, while being smeared thoroughly with the sticky pulp. Then they would look very comical and human-like while trying to rub off the stickiness on their faces with their front paws very vigorously. They would adopt various acrobatic postures while feeding – a common one is hanging upside down using their tail as an anchor over the branch while feeding on some fruit or flower with their front paws. Once a curious juvenile common langur approached close, while the squirrel was hanging upside down and feeding on the strong smelling Careya arborea flowers (the nectar and the fleshy ovary). To my delight and astonishment, the langur suddenly reached out and gingerly patted the squirrel on its tail, it looked around and did it again. The squirrel continued feeding, unperturbed and oblivious. The cheeky monkey hung around a bit and getting no response scampered off.

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During my observations, it was important to figure out the exact plant part they were feeding on. For example, I thought I observed them feeding on Buchnania lanzan (Chironji) flowers. But on a closer look, I realized they were actually only feeding on the flower peduncles. I also observed squirrels licking termite-infested bark and eating soil on some occasions. Squirrels fed on sprouting and mature leaves of Mangifera indica, Syzigium cumini and Ficus glomerata (Goolar)and mature leaves of Terminalia arjuna and Tamarindus indica (Imli or the tamarind tree), but it never was a very important part of the diet. The bark of species such as Terminalia arjuna, Mangifera indica, Terminalia bellerica, Careya arborea and Madhuca indica (Mahua) were fed on. They would strip off the outer hard covering and eat mainly the softer phloem/pith inside.

As summer approached, there would be a lull in the morning feeding frenzy and the squirrels would take time off to rest by early afternoon. They would sometimes lie spread-eagled on their belly in the shade, on the lower horizontal broad branches of an Arjun tree. One one occasion, it was an amusing sight to watch a langur also resting on its belly with its arms, legs dangling down just a few metres from the squirrel on the branch. Two species sharing space and resting together amicably as companions. I so used to wish I had a good camera on those occasions.

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The giant squirrel is a solitary creature, but had overlapping ranges. There would be different kinds of interactions among the squirrels depending on the sex and age/status of the neighbouring animals. Many preferred resources were rare in the habitat, and the spatial and temporal variation in food supply resulted in overlap between individuals at locally abundant food resources. The defence of an exclusive area guaranteed of resources throughout the seasons is not possible. So, squirrel ranges overlapped, and encounters were often avoided by spatial time-sharing. But when encounters occurred, there would be aggressive territorial chases, if a neighbouring squirrel came too close. But at superabundant food resources like on a tall Semal tree, it was a common sight to see up to four individuals feeding at the same time on the flowers in March. Initially, I was surprised that there were no aggressive interactions, but I soon realized that even here they maintained some distance (5-10 m) from each other and sat and foraged in their own space on the tree and if any individual came close, there would be a chase. This Semaltree was also on the periphery of the core ranges of a few squirrels and therefore they seemed to tolerate each other’s presence. This tolerance could be also related to some dominance hierarchies that existed which resulted in fewer overt aggressive encounters. For example, the sub-adult male I followed, showed in several interactions that it was subordinate to the other two adults.

This semal tree was also located where there was a substantial break in the canopy and it was just away from the edge of the riparian habitat. Any squirrel needing to approach the tree, had to make a considerable leap from the nearest tree. Many a time, I would watch in trepidation hoping they would not fall. Towards April, when several of the squirrels had their pups, I watched the mother coaxing and teaching her pup to jump. The mother jumped first and turned around, waiting for the pup to follow. The pup reached the edge and kept hesitating, and turned back. The mother again jumped back and approached her pup and then jumped across as if to show the pup how to do it. Finally, after several attempts, the pup jumped and thankfully made it. I observed many other interactions between the mother and pup. Studies show that the pups stay with their mothers for 8 months to a year.

Giant squirrels are believed to be completely arboreal and and need canopy continuity in the forests they live in. However, one part of my main study site was in a disturbed area with several breaks in the canopy and a major one where a road cut across the nala. On several occasions, I saw giant squirrels coming down to the ground to cross small stretches where they had no choice. Although this is risky for an arboreal animal, for me it was heartening to see that some individuals in the population had the ability to adapt in a disturbed habitat. Their diet also indicated their adaptability – on the edge of the riparian stream, there was an open patch, with cleared fields and some lines of planted exotic trees of the Australian acacia Acacia auriculiformes, and Peltophorum ferruginea. Before starting my study, I was under the impression from earlier work, that they were extremely dependent only on continuous dense undisturbed forests. So one fine day, when I had to follow my focal animal into these trees and it started feeding on the flowers of these exotic tree species, I was surprised but kind of happy that these animals were flexible and had the ability to adapt to human-caused changes in their habitat.

I recorded some very unusual behavior during the six months. In the winter months, there was very little to eat in the undisturbed riparian habitat in terms of unripe fruits/seeds that squirrels mainly eat. Although they include flowers, flower peduncles, bark and leaves of some species, the main resource is seeds. Given the low resource availability in the habitat, I expected that the squirrels would move around a lot more, searching in new areas for more food or that they would make a dietary switch to eating more leaves and bark. Instead, to my surprise, they spent very long hours simply resting and basking in the daytime and very little time actually feeding. Though occasional forays were made, these were of short duration and no food was located. This was in the winter months during peak feeding time. In the same period, the individuals I followed in the other area were feeding voraciously on the abundant seeds of Arjun and other species. So, it appeared in times of food shortage, instead of switching their diet or moving more to find food, these squirrels adopted a strategy of conserving energy by minimizing their requirements by resting. In addition, food items like leaves and bark are eaten for particular nutritional needs and a dietary switch to eating more quantities of such food would require more energy in terms of processing; bark and leaves are harder to digest.

I recorded another undocumented behavior during April-May when the daytime temperatures soared above 40 degrees. The squirrels started spending long hours in the nest in the daytime, soon after 9 am. The first day this happened, I was flabbergasted, and wondered what was wrong. Had I approached too close, was the animal disturbed by my presence, I worried. Then over the next few days, it happened with all the three individuals I was following.  I also noticed the non-focal individuals in the area doing this. They were all going into the nest at around 9 to 10 am and coming out only after 3-4 pm to do some quick feeding before dark. I was left wondering what had gone wrong with these chaps. It was especially surprising because I spoke to a couple of biologists who had studied giant squirrels and they had never observed long periods of daytime resting inside the nest.

Why weren’t they feeding? Or why weren’t they simply resting outside in the shade of the canopy. I had no proper evidence but from watching their behavior over days, I hypothesized that possibly it was too hot to spend the time foraging and instead of resting for such long periods outside on branches where they may be at risk of predation by several raptor species active in the mid-day, they chose to go into the safety of their arboreal leafy homes.

There was a fair bit of excitement during my study as I observed three unsuccessful predation attempts by the crested-hawk eagle on giant squirrels. One of the attempts occurred, while I was observing a squirrel feeding on Terminalia arjuna seeds. Two other squirrels were feeding on the same Arjun tree, while on a nearby Bombax ceiba (Semal), two more individuals were feeding on the flowers. A crested-hawk eagle flew in and perched on the tree. It did not seem to be hunting actively. Two squirrels immediately mobbed it by approaching close and giving loud alarm calls repeatedly. The hawk-eagle responded with wings outstretched, but seemed unperturbed and did not attempt to catch them. After a while one of the squirrels left the Semal and was moving slowly along the branches of a Terminalia tomentosa (Saj or the Crocodile bark tree) when the eagle swooped down in an attempt to catch it. The squirrel, instead of fleeing, immediately turned around and faced the predator and gave alarm calls. In the meantime, the other squirrel on the Semaltree had also moved onto this tree and started mobbing the predator. The three other squirrels on the Arjun tree also started alarm calling. The hawk-eagle made a half-hearted attempt to catch one of the squirrels and then flew away through the canopy. It was surprising to see five different squirrels ganging up on a predator together.

I observed another predation attempt one afternoon in March while following a focal animal, which was resting inside its nest. There was another another focal squirrel (the sub-adult male) on an Arjun tree across the nala. It had come out of its nest and was resting on a broad shady branch. A crested-hawk eagle flew in and made an attempt to catch this individual. It was unsuccessful, and the squirrel reacted to the raptor by giving loud repeated alarm calls and ‘mobbing’ the hawk-eagle. The squirrel approached the hawk-eagle as close as 1-2 m. The crested-hawk eagle spread its wings six times in response to the mobbing by the squirrel. It made a second attempt to catch the squirrel with wings outstretched. The squirrel called, moved down 3 m but again approached the hawk-eagle. The crested-hawk eagle watched the squirrel but appeared disinterested and even started preening its wing feathers. The squirrel kept the predator in sight and then after a while it retreated to a lower branch, some meters away, continually giving alarm calls. Some time later, the squirrel was not visible anymore since it had moved behind the trunk. The crested-hawk eagle was still perched on the tree. After a while, I saw another squirrel moving onto the tree that did not notice the predator till it was very close. The hawk-eagle spread its wings and flew away. This squirrel gave alarm calls and then started resting on the same branch.

I observed the third predation attempt by an immature crested hawk eagle on the sub-adult male squirrel on one morning. The squirrel immediately started loud alarm calling, faced the eagle and approached it close instead of trying to hide or escape. The hawk-eagle seemed to have given up, and perched on a branch and started preening its wing feathers seemingly disinterested (displacement behavior?). When the squirrel approached it too close, it responded with outstretched wings but did not attempt to catch it.

On all these occasions, the squirrel which was attacked responded by ‘mobbing’ the predator. In a behavior which seemed suicidal, they approached the predator very close and gave repeated loud staccato calls in full view of the predator. This behaviour was seen only when a predator made an attack or when the squirrel was sure the predator had seen it. But on occasions when raptors flew overhead, squirrels refrained from giving any alarm call and remained quiet by either becoming alert or flattening its body against a branch. Squirrels gave loud alarm calls mostly when the predator came very close. This behaviour suggested that that the function of alarm calling especially in a solitary species is a signal to the predator. This is supported by the fact that the raptor seemed to be startled by the prey’s response and did not attempt to catch the prey after the repeated mobbing. It could also be speculated that the predator was an immature eagle, and therefore, the squirrels approached close and ‘mobbed’ it or that it was not hunting actively. Other studies in Africa and North America have also observed that squirrels mob inactive or immature predators where the squirrels do not seem to be frightened and give repeated alarm calls even when the predator is very close.

I have fond memories of those days spent watching the giant squirrels. It was my first foray into real field work and my first field research study and I fell in love with squirrels. My only grouse with watching them was the crick in my neck from standing and looking up into the canopy all the time. So, every opportunity I could, I would try to lie down to watch them. I also got used to involuntarily always searching up in the canopy. When Dr. Johnsingh and Dr. Goyal came to visit the field site, I remember Dr. Johnsingh yelling at me while on a drive: “Appu, stop looking up in the canopy and concentrate now on looking for the terrestrial mammals” – his beloved sambar and other creatures.

That training was useful in future years as I was doomed to a lifetime of field work that constantly involves looking up in the canopy for arboreal animals (squirrels and primates to hornbills) in north-east India. In later years, I moved onto studying the various squirrel species including a cousin of the Indian giant squirrel – the Malayan giant squirrel in Arunachal’s tropical forests. But in these dense hilly forests where the animals have faced hunting pressure, I could never follow and watch the squirrels for long periods and I had to be satisfied with fleeting glimpses. All I could do was count them on transects and obtain some records of their diet/habitat use. But the sort of insight and understanding that one can get from really following an animal and watching its behaviour over days/weeks and months is impossible to obtain from the  indirect methods that we mostly use to understand the lives of many species.

A shorter version of this article had first appeared in JLR Exlpore online in October 1, 2016.

I published my first research paper and a couple of short notes from this work though I never ended up publishing some of the main aspects of the study. 

1. Datta, A., and Goyal, S.P.Comparison of forest structure and use by the Indian giant squirrel (Ratufa indica) in two riverine forests of central India. Biotropica 28 (3): 394-399.

2. Datta, A. Anti-predatory response of the Indian giant squirrel Ratufa indica to predation attempts by the crested-hawk eagle Spizaetus cirrhaetus limnaetusJ. Bombay nat. Hist. Soc. 95: 332-335.

3. Datta, A. Daytime resting in the nest – an adaptation by the Indian giant squirrel Ratufa indicato avoid predaton. J. Bombay nat. Hist.Soc. 96 (1): 132-134.

 

 

 

 

 

 

 

2 thoughts on “Unlikely giants of the forest canopy

  1. Such a lovely read! I have mostly seen fleeting glimpses of the ones in northeast India, so it is really nice to get some new insights into their habits.

    Like

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