At about 9 am one April morning, three field assistants and I walked along a trail in Sunkadakatte range, Nagarhole Wildlife Sanctuary, walking in even paces and counting them. We were measuring habitat parameters for a study that determined where flying squirrels were found in the Western Ghats of Karnataka. Was the Indian Giant Flying Squirrel found in all forests, or did it have a preference for specific kinds of stands?
The Indian Giant Flying Squirrel (Petaurista philippensis), one of the two species found in the Western Ghats, is one of the largest flying squirrels in the world, with gliding membranes between its wrists and ankles as well as between its legs and tail. With the lift provided by both of these, the species can glide up to 250m and even up to 400m on a down-slope. Flying squirrels are nocturnal, and inhabit forested areas.
To determine the squirrels’ preferences, we set circular plots of 11.3m radius, every 200m, to the left and right of the trails that we spot-lighted at night. In these plots, we measured heights and girths of all trees, the number of trees, what flowering and fruiting states they were in, and the species. Also important to know was how connected the canopy was, a data point determined from how interlaced the trees were.
As we were measuring a large Terminalia arjuna tree, we heard a noise from above – a flying squirrel had run out of a hollow on the tree trunk, and up a branch. It paused and looked down at us, alert, its body hunched-over and its tail held up over its body. As I fumbled for my binoculars, it ran further along the branch, and glided off the end to a tree 30m away. Landing on the trunk, it went up into a hollow, going from hollow to hollow in less than a minute. Almost immediately, there were loud growls and snarls from this hollow, and one flying squirrel – presumably the one disturbed – shot out onto a branch, while another looked out of the hollow at it. After a brief face-off, the squirrel again moved upwards to the perimeter of the tree, glided to a second tree, and disappeared into a hollow. The second glide, over 100m long, was virtually over our heads, and gave us a view of the animal at its best. While glides at night are shadowy and mysterious (tracking glides at night is about shadows, following eye-shine, and tracking sounds of the landing), watching a flying squirrel glide in broad daylight is a spectacular sight. As it whooshed overhead, its patagia (gliding membranes) were stretched out to the maximum, billowing slightly, and translucent against the sun, with an intricate pattern of red veins showing through.
A survey across the Western Ghats found that the Indian Giant Flying Squirrel was present in various forest types, from dry deciduous to evergreen rainforests, as long as forest stands were tall. Gliding is the primary mode of locomotion for flying squirrels, and they require tall trees to glide from, in order to move in an energy-efficient manner. The taller the take-off point, the longer the glide; they are not powered fliers, and merely drop in height from the take-off point to the landing point. During this study, flying squirrels were not seen in scrub forests or high-altitude stunted shola forests within grasslands. Both of these habitats lack tall trees. The Indian Giant Flying Squirrel is found all the way from low-elevation forests in Karnataka to high-elevation places like Kemmangundi – I have heard flying squirrels call in tall coffee plantations and evergreen forests in the Baba Budan hills, at a height of 1300m.
Our study noted that flying squirrels were also partial to the girth of the trees in a forest, and were not seen in stands with small trees. They use tree hollows to sleep and rest in during the day, and each animal uses 1 to 6 hollows at any given time, moving between hollows even every night on occasion (known from studies of other species, and the Travancore Flying Squirrel in Kerala). This might be one of the reasons they are particular about the presence of tall and large trees, as these have more and larger cavities. The hollows they use are typically on the trunks, and can be natural (created by fallen branches or wood rot) or artificial cavities (created by species like woodpeckers or borers). I have seen a flying squirrel chewing out and expanding a cavity in evergreen forests in Seetanadi, but beyond occasional anecdotal observations, we don’t know how often flying squirrels create or modify the hollows they use.
That morning at Sunkadakatte, I also realised that the displaced flying squirrel had clearly known where to go for shelter, and which trees had hollows – there was no time lost searching or fumbling, implying that these animals have a spatial map of their surroundings. What it did not know at the time was which hollows were occupied, or who occupied the hollows.
While we now know a fair amount about the habitat requirements of flying squirrels and their occurrences, at least in the Western Ghats and some parts of the Central Indian landscape, we know little about their behaviour, social structure and mating systems. Maybe over the coming years, more researchers will study these elusive creatures, helping us understand them better.